I've never replaced the belleville washers, but I guess they could wear out. They don't move much between compressed and relaxed, I think someone told me it was something like 20 or 30 thou.
All I usually do is make sure the face of the adjuster screw is flat, then replace all the O rings.
Reg testers, I bought mine from Joe Korick, so I can't say on how difficult they are to make.
"I'm your huckleberry, that's just my game"