Do you have the foot stomp starter switch ?
If so, it may not be the starter but the starter switch. This starter switch sits on top of the starter and is held on by two 3/16 screws. Remove the switch and turn it over to see if the copper parts of the switch are corroded. If so, clean them up.
Another item to check is the solid copper plug that sits atop the starter underneath the switch. make sure that is clean and not badly worn.
Just my 2 cents.....
