Hi,
# 8 it is a dust cap, which is held with a Segerring, should not be loose, remedy, remove the rear shaft and remove the bearing and dust ring, measure and possibly put a spacer in between
Only tighten the clamping nut of the front propshaft by hand
Maybe you are also interested in a better gearbox
I have a six speed classic gearbox offering speeds up to 2000 rpm at 60 mls
best regrads
Tom