I had a few issues with my air suspension as well, since 40k they have swapped both front airbags and a few fittings. When they replaced the right airbag it didn't fix the problem as there was a pin hole leak in a fitting. They troubleshot it for 3 weeks and finally fixed it. Things have been fine for the past 30k.

FYI- ALL air suspension components are covered by the CPO warranty, my dealer tried to pull a fast one on me and the BMW engineer that came out to authorize more labor hours confirmed that the Air suspension is not a wear item and is covered for 6 years or 100k.