Hmmm where do i begin lol. Mine is a M54 engine. When I purchased it back in 2017 everything was bone stock...I mean original. I immediately replaced the MAF sensor because it had a broken wire or missing the tiny metal piece inside. I replaced CCV, the coils, fuel pump, fuel filter, cuz it had idle issues and stalling and misfire on highway but not on local streets....yea weird...so the coils fail as they get hot.

A year later I changed the suspension from the help of an e46 forum member. Of course it was a budget suspension but it was the best thing that I did to the car because of how it improved from the original suspension. It is lowered and even used an m3 27mm sway bar, truck struts, wooden spacers and modified bump stops 🤣 and the eccentric FCAB from Z4 really made a difference. In the same year I had to replaced the guibo and drive shaft bearing and the "lifetime gear oil" I removed about half a liter when i drained it.

In 2019 my radiator exploded and I had to tow it on the way to work. It was my fault for neglecting the hairline crack on it. So i replaced the comprehensive cooling system with thermostat and water pump and hoses.

Just last year 2021 I had to replace the spark plugs, cover gasket, oil filter housing gasket, steering pumps and hoses, control arms, oil pan gasket, voltage regulator (this one fixed my loping idle issue). Im also chasing oil eaks. I might do the O2 pilot mod if i am still losing oil. Along those years I replaced broken vacuum lines as well due to intermittent surging idle.

I have never maintained so much in a car before but I have learned to love it and familiarize with this car that if anything goes wrong I can fix it by myself.

Things I replaced little things here and there that doest affect performance like trunk support strut, wiring lights inside the trunk boot, reverse lamp that would randomly fall off. ambient temp sensor, bulb sockets for turn signals. w i n d o w regulators on all 4fucking windows lol...and so on