80's mercury help finding parts w/serial #

just bought boat a few months ago and starter just went out. I live in illinois so don't need a title with motor, so I did not get one. I was told it was early 80's. Anyway I have been trying to search for parts with no luck. My motor has only 7 digits and no letters. Can this be right? I read on some web page that there should be a letter after first #. Any help getting my boat on the water would be greatly appreciated. It's a 2stroke 40hp and it's says somewhere on motor thunderbolt ignition. Serial #5175221

you can call merc in fondulac , they will tell you what year it is then you have a place to start

Your motor is a 1979

Redbeard, you can get parts on crowleymarine.com, iboats.com, or from the mercury parts express site. I actually have that same exact motor and I rebuilt almost the entire thing. If you have access to a Mercury dealer, I'd go to them first. Parts are readily available for this motor and it is very simple to work on. It is a fantastic motor and pushes my 16 ft v bottom jon like a champ. If you have any other questions about issues with your motor, just let me know and I'd be glad to help you out.

Also, eBay has some really good prices on starters for these motors. I'd check there and compare with other places.