[Stock328xi]

A lot of work you may need (regarding the leaking valve covers and oil pans) are not that bad, as i do more at the shop ill post quick how-to's. While I know they are out there, new ones people don't need to search for can be useful.
Other than that, keep track of what you have done to your car and what happened during when something started acting up, and a side shop (like a BMW specialty shop) will like it more. It's like going to the doctors, if you don't tell the whole truth it can be a bigger issue and cost more at the shop.
We just had a kid bring his car in for diag after doing a good amount of work, but didn't tell us the full truth about what had been done to the car, so more time was wasted because we went into it blind.
If you have more money than knowledge in working on these an aftermarket warranty is nice, but if you get down and dirty working on your bimmer (and do the work properly ) then I'd recommend doing that.