I'm a bit late in addressing this, but . . .
When put the cush drive nut on, I assumed it was just like my M20 with a washer and cotter pin to keep it from coming loose. But a look at my Hayne's guide shows a lock nut with a cotter pin. Please, someone tell me I don't have to go searching for a nut. Hell, if a washer was good enough to win WW II, it should be good enough now!