That rivet holds a collar to guide the shaft
and should be there. Not everyone was a
fan of this reversing mechanism and there
was a verity of ways to lock them in the
forward position. That was the purpose
of the 2 brass screws in the unit I posted
earlier however welding is more common.
Has someone welded your shaft to the
collar to accomplish this and that’s what
making you think it has been broken?
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.