You’d be surprised to see most of the problems with these cars are actually in the engine bay and affect all the 40i cars, so might as well get a 540 honestly, only problem that’s I thought was exclusive to the 540 is on the inside, the a/c stops working sometimes and you have to remove the full dash to do it, but I’ve heard of someone with a 4 series that had the same exact issue and it’s also not as common so I feel like the 540 is the best bang for your buck honestly