I researched the Moyer site a while back and think the price for a rebuilt a bit steep.(something like $4k) You will also have to pay shipping for both sending your old motor for exchange and for shipment of your rebuilt. In that they are on the east coast, that's probably going to be expensive.
The old A4's are a very simple engine, much like the old Cris Craft K engines from the 40's. Seems like any good engine rebuild shop should easily be able to rebuild one of these. They probably would have to get any needed parts from Moyer. A fellow sailor in my marina had the same problem with his.
Last I knew, he was researching the options for re-installing a small diesel (used) for not much more cost than the rebuilt A4. Food for thought.