As Lee noted, there is the air ride system for on the road, and then there is the (optional in 2004) air leveling for when parked. You said “air ride” in your initial question. With that in mind, I’ve sometimes parked temporarily in a slightly sloped lot with the steering wheel turned, and noticed one front side appeared lower. A tech told me that happens sometimes depending on slope, wheel angle, and when the engine is turned off in the process. It goes back to level travel mode when I get underway again.
If the front ride height adjuster’s rubber “boot” gives out, the whole front end should fail to hit travel height, not just one side (re. Eric’s reference, a 2004 Monterey should have one front valve like Lee states). The adjuster part is RN10JC by HALDEX. But it’s worth checking; see pix below.
If you look in the Coach Assist part of the Members Only section on the Home menu here, you may find manuals and materials with assistive information.
As Eric mentioned, don’t be foolin’ with air components under the coach unless you’ve properly blocked it.
Joel