I lost a tooth on the sliding gear in my CP. Fortunately, the tooth simply ended up suspended in the grease without causing further damage. That said I was never aware of it happening.
I guess this sort of thing must be pretty rare though. These boxes were used by Vincent so are pretty sturdy, as well as AJS. It is however a sobering thought since, the box can't be disengaged from the rear wheel as it can from the engine, by the clutch.
AOMCC Member 4296
1950 Rigid Ariel VH
1951 Rigid Ariel NH (under construction)
1973 Norton 850 Commando Interstate