Hey guys, I'm back.
A new solenoid did the trick on motor #1. Sticky bendix on motor #2, I've brought it home for clean & lube.
In the course of this adventure, I'm thinking the batteries are not wired in the proper series. There are two starter batteries (port & starboard) and one deep cycle. There is a battery combiner, and the previous owner has wired it between the port motor and the deep cycle. I'm guessing this was done to apply an alternator charge to the deep cycle(?).
Honestly, It's an older boat and I'm not sure the combiner works. I've a mind to isolate each starter battery to its own outboard, and leave it at that. Any thoughts? thanks