The good news is yes , any auto electric shop that can rebuild import starters can rebuild your Duc starter.
More good news is that Chris at ca-cycleworks just posted somewhere that he has a quantity of left side cover gaskets (usually unavailable from most dealers). I think it's the "No More Slime" thread. The bad news is the shop is closed for the holidays, but you can send in orders to wait for his return.
Do you have a Haynes manual to guide you? Even if you have a post-96 model, the internals are pretty much the same on the 6XX, 750, 900 models and the manual is a great reference.
Check the flywheel nut and inspect the wires from the alternator for signs of insulation trying to melt while you are inside the cover.