Been selling new and parts for 20 years and I can honestly say that one is alot older than that.
I would put pretty good $$ on the fact you won't get straight swap after market parts, but....
If it's loosing grunt it would probably be the motor, all you can do is try and take out and see if a motor re-wind place can do something.
But, good luck getting it out!!!!
If needed I have a Maxwell sittin g here for very much the right price, 10mm chain but no rope winch
