water in transmission

Water has been leaking into the transmission (manual) of my 91 Z24 (3.1), from the back of the motor. How is the water getting there; that is where is it leaking from, and how do I fix It? For anyone who wants to know, I pulled the transmission for the third time in as many years (not to mention the time mechanics replace the first clutch) only this time I yanked the flywheel. Low and behold, one of the three frost plugs was leaking. The worst parts is I took this problem to the dealership when I first bought the car. The leak at that time was so small it took 7 or eight months for the fluid to get noticable low (in the reservoir tank) and there was a small mess under the car after 3 or 4 years. Needless to say I now have to pull the frost plug out and replace the transmission. For those who have done this wish me luck as it is very labour intensive for a single individual. Bye, la revedere, Calus.