I have rebuilt a few. The most common problem is a warped air horn gasket surface. The second worst is the small float size, which doesn't provide much pressure to the needle valve so it tends to hang up. I found that using a steel ball bearing and a punch to round out the seat really helps with the life of the needle valve. (Thanks for the tip carbking).
The final problem I have run into is the power piston sticking. It needs to be clean, and if it is tarnished hit it with some brass polish to clean it up so it slides nicely. (This is a common problem with qjets and 2G's too)
