1978 Alpha One drive Merc 228 that seems to have a bad prop shaft seal or bad prop shaft. Had it to a dealer and said they pressure tested the lower after replacing the seal, said the prop shaft was worn by fishing line. I'mma do this myself so besides getting a manual what's it take to get the prop shaft out and replaced? I can get replacement parts and my mechanical abilities are up to par, but what am I actually looking at here?