Six months ago I got 2001 with 110k miles. The system was leaking and at first I tried a rebuilt valve body.That made no change at all. Then I saved up and got the genIII air springs which helped some. I also reprogrammed the computer to take advantage of the additional height capability of these springs. I think these ride better too.
Leaks persist though and last weekend I replaced the air tubes which go to the front springs. That was a mojor improvement, but now the rear sags overnight, which looks even goofier than the front springs sagging while parked. Probably will replace rear tubing this weekend.
So I have ~$1500 in parts but am expecting it to be good for another 100k when done.
Randall