Just wanted to share a positive experience we recently had with the X5.

Short story: replacing the air suspension components seriously firmed up the ride and made the car drive much tighter. Total cost was <$500.

Longer story:

2012 X5d with ~85k miles. Despite new b4 shocks the ride felt loose and we felt it the truck was beginning to "showing its age" despite having all the bushings/mounts checked out and a re-alignment. Just felt like there was extra body movement when going over bumps/ spirited driving.

The rear air suspension recently failed (both sides of rear lowered and not going up despite air compressor running). I replaced the bags first (seemed like the most common failure point), but the culprit turned out to be a weak air compressor. I was trying to minimize downtime and ordered all parts from Amazon, which turned out to be the most cost effective source for the bags and compressor as well.

After replacement of the airbags and the compressor, the X5 drives much tighter with less lateral movement over bumps. It literally feels like the SUV has new/stiffer springs.

HTH