those Volvo integral starter/generators haven't been made in a long time and there are no replacements, you'll either have yours rebuilt or find another old one that has been rebuilt. If your shop is familiar with them, is clean and reliable, go with it. The frames never wear out, the bearings and wiring can always be replaced. The only question is the quality of the workmanship.
In future? All you can do is try to pick up a spare.