I have one of those units here and the back of the motor housing just
unscrews. The joint is right at the red strip. You may need a strap wrench.
I just tried to do it by hand and this one was too tight. However, the cone
portion of the housing unscrews and the wire coming out of the end of the
cone should start slipping.. If it doesn't, after a turn or two, try pushing
it into the cone until stops rotating with the cone.

Inside you will find the replaceable electric motor.. It is this motor that
is standard spare part for all of the old AH and ST wheel and tiller pilots.
Even the enclosed wheel drive units had the same motor (so I'm told).

If you do a gooble search of this NG or the rec.boats.cruising you my find a
few posts about this motor being a recommended cruising replacement.

Steve
s/v Good Intentions