i just bought my first boat and it wouldn't go into reverse or would grind and clunk a bit.i checked it out a bit,found the linkage at the motor was not hitting very well so i adjusted it till the ball was setting firmly into the linkage arm at the motor.it still acts the same, i asked a few friends and they seem to think its the lower end gears...any other guesses?it is a1990 johnson model#tj40elesr and according to the letters it is a 20'' shaft.i checked prices and what it would take to repair it and one of my?'s are i found a few lower end units for sale but some say short shaft some say long shaft.whats the diffrance?also are their any cutoffs on years like 1935-1964/1965-1999?and if i plan to keep this motor what is my best bet if it is the bottomend gears?