As I recall the pad clearance adjustment is made using a socket wrench on a nut (?) accessible from the front of the caliper. I guess that pads can be replaced without removing the caliper from the rotor (or from the MH entirely, but I think it would be pretty difficult). The caliper is rather primitive and has one movable pad and one fixed one. "Adjusting" the caliper means turning the adjustment nut so that the pad grabs the rotor enough to hold when the brake is engaged.
If you have found that one of your pads is completely worn through I suggest that you verify that the brake is actually fully released even though the warning light is off. We ended up having a catastrophic failure of the air actuating chamber, but I'm pretty sure we had a progressive failure of it long before it blew entirely. The evidence of this was two sets of pads having been worn out in ~3 years of driving even though I know I never drove with the parking brake on. I'm pretty sure mine was dragging long before it failed.
BCS does have parts for this brake, but they aren't inexpensive (but then again, what about a Beaver is?)
