i do not have air suspension but i hear they have these problems pretty common.
they actually make airsuspension delete kits so that you can revert to a no-service spring.
BMW x5 x6 E70 E71 E72 Rear Suspension Air Bag to Coil Spring Conversion Kit | eBay

but it seems new airbags are cheaper
Rear Air Spring Left LH or Right RH for 07 12 BMW x5 E70 Sport Suspension | eBay

Rear Air Spring Bag LRRR for 07 11 BMW x5 E70 with Standard Suspension | eBay

BMW x5 E70 x6 E71 E72 Air Ride Suspension Rear Air Spring Bag Assembly Pair | eBay