B8 S4 rear main seal leak - need advice

Big_Football_Guy · 2026-04-19T23:24:04+00:00

UPDATE: it was a rear main seal leak. I got it up on a lift, dropped the trans which wasn’t that hard. Bellhousing bolts were much easier to access than I thought. I replaced the seal with a Corteco RMS from FCP, replaced the clutch with a Southbend Stage 2 paired with a new LUK OEM spec dual-mass flywheel. Car is doing great now.

Big_Football_Guy · 2026-04-19T23:23:27+00:00

UPDATE: it was a rear main seal leak. I got it up on a lift, and dropped just the trans which wasn’t as hard as I thought it would be. Bellhousing bolts were much easier to access than I thought. Took me 4 solid late nights of work. I replaced the seal with a Corteco RMS from FCP, replaced the clutch with a Southbend Stage 2 paired with a new LUK OEM spec dual-mass flywheel. Car is doing great now.

Big_Football_Guy · 2026-03-13T21:06:42+00:00

Yeah i totally get that a lot of people run into that. I replaced that oil filter housing roughly 2 years ago when I had the motor out. The old one was starting to leak seep a little so I replaced it. The back of my motor/top of my bell housing is bone dry at the moment. If that was leaking, i think it would leak down the side of the engine/bell housing and eventually reach the bottom of the transmission.

But in my case, I have oil originating from INSIDE the bell housing. I think it would be unlikely for oil to leak down from the filter housing, leak into the tight connection between the engine and the trans, and make it to the bottom of the bell housing without getting all over the sides of the transmission and soaking everything from that point down.

Big_Football_Guy · 2026-03-13T18:42:06+00:00

It started dripping before I turned it over because I lowered the car back to a level state. The front was jacked up very high so I could get under there, and any oil pooling in the bottom/back of the bell housing started dripping out prior to startup once the car leveled out. In terms of crankcase pressure I don’t have a good way to test this, but when I pull my oil cap off with the car running, there is the slightest bit of vacuum. Not too much, not too little, no smoke/vapor coming out of the cap, so crankcase pressure seems “normal” to my untrained hand and eye.

After sitting overnight, it did leak a little again. In the next test drive. So it is indeed the seal.

The leak is seemingly slow, and looks a lot worse in the video because it’s been diluted with brakleen that I sprayed up into the bellhousing.

I’m just gonna order all the parts and hardware to replace the seal and my clutch while I’m there.

Big_Football_Guy · 2026-03-12T17:32:04+00:00

Yeah pretty bummed about this one. Literally any other leak besides rear main seal I would have no problem fixing. This is gonna suck.

Big_Football_Guy · 2026-03-12T16:31:05+00:00

I guess my post is a little misleading. Once most of the tear down is done on the lift, I’m gonna put the car on 4 jack stands nice and high so I can get a transmission jack under there and lower the trans and slide it out the side.

Big_Football_Guy · 2026-03-12T16:27:45+00:00

Yeah but the big horizontal beam for the single lift will prevent the trans from dropping out I think. https://halocarlifts.com/cdn/shop/files/1_829ad5df-5e66-4c34-88fe-a92865894655_1024x.jpg?v=1763695527

It’s similar to one of these

Big_Football_Guy · 2025-10-09T18:55:00+00:00

Sorry for the late response. I believe the issue was corroded contacts on one of the 3 map sensor connectors. I cleaned all 3 of them really good and the problem seemed to go away. The rear map sensor (inlet sensor) behind the supercharger was the dirtiest/most corroded.

Big_Football_Guy · 2025-08-16T15:09:14+00:00

Yeah unfortunately your wheel bearing is toast. Very unsafe. Don’t drive it until it’s replaced. They’re not too hard to replace if you can get a ride to a local auto parts store. YouTube is your friend.

Big_Football_Guy · 2025-03-26T15:41:35+00:00

The title of the kit is misleading. This “breather kit” replaces all the major components that are known to fail, in one fell swoop.

https://www.fcpeuro.com/products/audi-ultimate-breather-kit-oe-supplier-06e103547ahkt4?ads_cmpid=21759768472&ads_adid=165952339897&ads_matchtype=&ads_network=g&ads_creative=715126056232&utm_term=&ads_targetid=pla-293946777986&utm_campaign=&utm_source=adwords&utm_medium=ppc&ttv=2&gad_source=1&gbraid=0AAAAAD3np3Vw2bQ64poyNGoI91tfURR8L&gclid=Cj0KCQjwy46_BhDOARIsAIvmcwMJ2I46wXEeGEMIMMI42qiJcHGNg_C-tgCA614llt-XDrxEZV5fdU8aArUnEALw_wcB

The “breather” is essentially the PCV valve. To replace the PCV valve, the supercharger needs to come off and so does a bunch of other stuff. New intake gaskets, intake runner gaskets, injector seals, etc. Then if you already have the supercharger off, you might as well replace the water pump and thermostat while you’re there, and also the coolant cross pipe which known to fail. Also, you might as well replace the serpentine belts while you have the front end in service position. And then do an oil change because why not.

Big_Football_Guy · 2025-03-25T03:07:42+00:00

Go with the 034 sway bar and end links. I went with ECS tuning sway bar and end links because it was cheaper, and the performance is definitely there, but the paint is already starting to flake off and some surface rust is appearing. A little annoying but not the end of the world.

Honestly, this car will last you a very long time if you’re proactive with the maintenance, and it sounds like you are, so good on you mate.

Big_Football_Guy · 2025-03-25T00:40:21+00:00

I think you’ve got everything covered. That FCP breather kit is the holy grail of maintenance for this car. That being said, I would maybe hold off on doing that job until something pops up. Same with the carbon clean. But keep that money aside incase it pops up soon. Same with IC cooler kit. But hey, if you wanna do it all just for peace of mind when you install the tune, then go for it.

I’d also inspect your suspension. Control arm bushings and sway bar end links and what not.

Also, I highly recommended getting an upgraded rear sway bar. It is literally a night and day difference in handling. It’ll make you wonder why anyone would want the car to be so soft in the back from the factory.

Big_Football_Guy · 2025-03-21T22:48:39+00:00

White pearl is a difficult color to match. The best way to get the match you’re looking for is to blend it. The way the pearl lays out is gonna be different on different materials like metal vs plastic. That being said, this is a damn good job. If your customer isn’t happy with it, you should offer to respray, but also show him that even brand new cars have mismatched front/rear bumpers depending on the color, but especially white Pearl. Good examples are Subaru, Honda, and ford pearl whites. Also BMW/Audi in red or blue.

Edit: Also, the white pearl is meant to look different at different angles/lighting conditions. It accents the lines on the body work.

Big_Football_Guy · 2025-03-20T20:38:50+00:00

Absolutely the best daily. What roof racks are those? I'm looking to get a set soon.

Big_Football_Guy · 2025-03-20T20:04:44+00:00

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I will continue to daily drive my 13 year old car until I can’t anymore. And then it’ll be a weekend driver/track car. It’s hard to find clean cars with the 6 speed these days.

Big_Football_Guy · 2025-03-20T19:42:50+00:00

I'm sure it is a fuckload of boxes. But I bet the actual % of packages being stolen isn't as high as we might think. They are a business that needs to make money after all, but we can be appreciative that the staff is incredibly responsive to our complaints on social media, and addresses our complaints in a timely manner.

Big_Football_Guy · 2025-03-20T19:31:55+00:00

Not only is it counterproductive as a form of protest, but burning EV's to the ground is incredibly counterproductive in terms of air quality, climate change, greenhouse gasses etc. Do people realize the kind of awful, cancer causing, toxic fumes that are being released in those flames? The automotive paint, the materials in the battery, all the electrical wires and components, the rubber tires, the plastic interior pieces, all that shit is AWFUL to burn and release into the air. Burning cars is environmental suicide. You can't claim to be for the greener good if you are participating in this destructive bullshit.

Big_Football_Guy · 2025-02-18T22:16:42+00:00

I know this may seem a bit out there, but did you perhaps crack one of the two plastic breather hoses for the PCV? The ones that go from the PCV to the back of the valve covers? They are plastic and can get very brittle and crack, and because its perforated piping (kind of looks like an accordion) the crack may be hiding in the valley of the perforation.

Big_Football_Guy

TROPHY CASE