SM465 Gear Oil

So, back to the '88 tow truck. I described in my earlier post that the ol' girl wouldn't shift (SM465) during my test drive. At rest, you can put it in any gear, however once moving, when it's time to upshift the stick doesn't move, like it's locked in place. Not grinding, just won't move. Once at rest again, it'll go anywhere. It also whined a lot so i determined my first course of action should be to change out the gear oil.

I've done some research and determined that I should be using GL-4 rated gear oil. I drained the old gear oil last night, was pleased to find no evidence of metal shavings mixed in, but no idea how old the oil is. It's an odd greenish to red color.

Waiting to pickup a gallon of GL-4 which is a little harder to find, but my local NAPA was able to get some delivered to me from another store today, it's Sta-Lube 85W-90 GL-4 rated.

So, first off, what's the best way to get a full gallon of this stuff poured into that little fill hole on the side? Can I remove the shifter and go from the top? Thanks in advance.

I used a handpump to get the fresh oil into the transmission. The one I had was designed for the lower unit on an outboard motor. It took a long time and was a pretty miserable job but it all got in there eventually.

There should be a better, faster pump out there but I used what I had.

I have found that a submersible 12v bilge pump moves hydraulic fluid nicely, but it has a 5/8" outlet. I bet if you were to cut the top off the gear lube jug, drop the pump in with the outlet necked down to 3/8", it would do a swell job of filling the trans with lube.