The load-leveling system on my 97 Ultra leaks down in a half-hour or so. When the car is parked after driving in the rain, I can see/hear air escaping from the bottom of the struts, so I know it's not a hose issue.

My question is, are the air-bladder struts a dealer-only item, or does Autozone/Advanced make a decent aftermarket replacement? How hard are they to change? Anybody done it on a '97-'05?

I just did a Search Forums (http://www.automotiveforums.com/vbulletin/search.php)for you and found a couple of threads that should help you:
Rear Strut Replacement on 98 PA - Automotive Forums .com Car Chat (http://www.automotiveforums.com/vbulletin/showthread.php?t=409907)
suspension overhaul - Automotive Forums .com Car Chat (http://www.automotiveforums.com/vbulletin/showthread.php?t=472661&;)