If you're going to try and match a belt (toothed belts are used everywhere these days) I can tell you from experience that the length of the belt is CRITICAL. Even imperceptible differences (too long or too short) cause the clutching mechanism to not work.
I threw mine in the sea (sorry Green Peace) after many attempts at trying to get it to work.
If you're doing any serious distance sailing, spend the money and get a new one. Repairs will let you down, it's just a case of when.