Sounds like a starter solenoid. The starters are pretty much bulletproof
but the contacts in the solenoid eventually get arced.

You can take the starter out, take the solenoid off it and open it up
(experience is worth its weight in gold here!) and clean/file the contacts.
There is potting over the screws that take the plastic end off the solenoid
and it also has two wires soldered into eyelets in the end. You have to melt
the solder to get it apart and then resolder them when you put it back together.
The two copper contacts (like 8mm bolts with funny heads) are held into the
end by what amounts to internally threaded washers. They are pretty hard
to get out the first time but you may be able to grip them with channellocks,
vise grips, etc and unscrew them off the terminals.
I cleaned the contacts on one solenoid 4 times before I ever had to replace
brushes on the generator, etc.
--
George Downs Bartlesville, Heart of the USA!