If you have the starter off, take it with you to the shop. They probably have the tool to remove , and replace, the "c" ring from the top. Pop off the retainer and replace the pinnion gear. Before you, or they, put the gear back on, check for tightness. I found mine was too snug and it didn't return like it was supposed too. I just cleaned up the gear with some 80 grit sand paper and it works fine now. Good luck!
Rich