The last two that I had rebuilt were for my '58 Bigtwins. I took them to a local shop that rebuilds all sorts of motors, alternators, etc. It cost me $100 each and the work was very good. Check with your local OMC repair facility - they will usually know who to trust with the work in your area.
I took my 1964 75hp starter to my auto mechanic and he sent it to his starter rebuilder. It needed brushes and various washers (spacers) and it was $80 at cost. It was totally gone over, cleaned and painted like new.
Before you spend 100 bucks, why is it that you believe the starter is toast?
What are the sypmtoms? They are OFTEN needlessly replaced, and you will not get a refund.
had mine built for 85 dollars works better than and arco i bought
but you may want to take it down sometimes you can clean them up
and get some use out of them .check before you spend the money to make sure its the starter ,the last motor i got was sold to me because it had probs with all the starters the guy had laying around . it had a soft spot in main cable corrosion and bad connections changed cables cleaned all conn,
fired right up went back and got the other two starters for 10$
so check it good before you spend the money .but i cant pull start my large motor so i had mine done for piece of mind.
good luck bennyb