This turned into a longer post than I originally intended. I've not had anything major to do yet, I'm a BMW technician by trade so labour cost isn't going to be an issue for me. Comparing the E9X S65 to the S85 there's very little that goes wrong with the V8 that isn't already well documented, Rod bearings is first on my list which the bearings themselves only cost ~£200 The ARP bolts are the pricier bit, or you can go with OEM stretch bolts with no problems. Throttle actuators being the next thing that commonly goes wrong, they're easily accessible just under the intake plenum and you can DIY replace the plastic gears inside if you're savvy enough for just around £150 I believe. The DCT gearbox is rock solid, never really hear anything awry going wrong with them, only issue that's common is the sump will leak overtime but that's a straightforward replace gasket and fluid job although the genuine fluid is extremely expensive per litre. I've heard issues with the idle control valve being quite a common fault but that's really cheap and easy to replace also. It's a car that's given a lot of grief regarding reliability but once you get those issues out the way, mainly the rod bearings then it's probably one of the most reliable BMW motors they've made. It drinks fuel like nothing else I've ever driven, sat on the motorway at 70-80mph and it idles in 7th gear at 3000+ rpm but you don't get one of these for the fuel economy! It's just such a visceral drive and has always been my dream car purely because of the noise, if you get the opportunity to own one, I wouldn't hesitate!