Just did this last week on my 93 5spd, filled with Redline MT90 75w90. Before this project the last drain and refill was about 4 years ago when I bought the car. That time I took it to Jiffy Lube, NEVER AGAIN! The Transmission drain bolt was stripped barely keeping its shape, and the filler bolt was even worse. I finally got the drain bolt off using a Craftsmen impact wrench and the required 15/16 socket. I applied a lot of pressure on to the drain bolt and held the socket on real tight to make sure it wouldn't strip what ever is left of it. After about 6 seconds of constant force from the impact gun the bolt finally came loose.
I left the drain bolt on hand tight while trying to loosen the filler bolt. I tried a regular 17 wrench open and closed ends with a 12" pipe on it for torque, and a 17 socket but the thing wouldn't move. Finally tried a breaker bar with the socket and that just stripped it even more and made it worse. Not sure what torque specs Jiffy Lube follows but I can tell you its way too tight and they stripped both filler and drain bolts. For anyone going to try this in the future..Use a regular combination wrench as it will prevent stripping that fill bolt. A socket has more chances of slipping off and rounding off the bolt edges when you go to turn that socket wrench.
Since I couldn't get the filler bolt off, I just took apart the shifter from inside the car and filled it from there. Poured about 1/8 quart and let it clean out any old oil left, put a new washer on the drain bolt, tightened it and then filled with 2.75 quarts of MT90 75w90. I must say MT90 is good stuff. I've put about 60 miles on it so far and the transmission feels so smooth, shifts are buttery smooth, no more notchiness, and the car doesnt feel as sluggish anymore. It actually feels like I gained power but really its the transmission working the way it should. There was even a small grind from 3rd to 4th but that went away after the first 27 miles of city driving on the new fluid.
This is a great write up and I recommend Redline MT90. While i was under the car I replaced the transmission mount, drained and refilled the diff with Redline gear oil, and replaced the shifter bushings with Marlin Crawler since I had the shifter out. I'll post about the mount replacement, diff drain and refill, and the shifter bushings in their appropriate threads.