Dave brought two solenoids to the boat but found that they weren't an exact replacement for those on the non-starting port engine--the electrical connects were different. So he took off the whole starter and we went to a shop in Norfolk called Auto Electric, known to be the local automotive alternator and starter wizards.  They immediately recognized our model and we were able to surgically extract the identification labels on the housing using a razor blade--they had been painted over with "Volvo green" paint. From that information we ordered a new OEM starter for about 1/4 the cost advertised by Volvo.

The shop also helped point out that our problem was with the pinion gear and shaft, explaining that the pinion should move freely along the shaft which it didn't . The workings were completely covered in fine rust dust and were seized. Guys in the shop suggested we "soak it real good in WD40 and then whack it with a hammer. Maybe it would free up."

After returning from the shop, Dave soaked the original starter in WD40 for a while, then freed it up by prying the pinion with a screw driver.  Lubricated, he reinstalled the starter and it turns out that was all it needed to work again. The engine started right up.  So now we'll have a spare starter!

Spare parts are good....