high mileage 4.8 vs 3.0 reliability
 

I currently drive a modded 335i and cts4 which im going to replace with a 2007 or 2008 x5 what im deciding between is the 4.8 vs 3.0. I like the power of the 4.8 but i know the 3.0 is probably a more reliable engine. But Besides the valley pipe issues is there any other major problems that are 4.8 specific.

valve stem seals... seems like a 'when' not 'if' issue.

Also the four corner self leveling air suspension can be problematic. When it works well the X is a pleasure to drive and ride in. If it has issues and you have to rely on a dealer or mechanic to diagnose and fix it can get costly quickly. A typical OBDII reader does not have the capability to diagnose or reset suspension codes.