Regarding the original cause of the corrosion.
I dropped a motor in the lake a few years ago while lowering it onto a boat. The lift rope parted. No one got hurt but the motor went under. I had a hold of it so it was only down a foot or so but I had to wait for help to get it out so it had a few minutes to fill. 1956 30hp johnson. I can lift them but not out of the water from the back of a boat.
We pulled it up, took the plugs out and cranked it by hand until it stopped spitting water.
Pulled the recoil starter off and blew the points dry through the inspection hole in the flywheel.
After that I put the Put the plugs back in and it fired right up. I ran around for 30 minutes or so to dry it out.
Everything worked fine for the rest of the season and we put it up for the winter.
Next summer…dead starter. Pulled the band off the brush area and horrible rust came out.
That little paper gasket was enough to hold water in there and over the fall/winter it rusted everything before it finally dried out.
The motor looks fine, no evidence that it ever went under. Still using it today.
I would lay money that the same thing happened to that motor. It went under, was pulled up quick and dried and cleaned thoroughly but, like me, no one thought to drain the starter.
I have a new rope on my lifter now.
