I've got a Yamaha 8hp two stroke ("The one-pull wonder") Never use the electric start.

To compensate for "prop walk" to port while backing I just swivel the engine to starboard.

I think docking would be real ugly at times if I couldn't swivel the engine.

Seems to me there must be some bad electrical activity going on in or around your boat to eat up an engine that much, even if it didnt have a zinc. Might also want to check the thru hulls