what gear oil do I use for my hearse??

Happy 4th of July everyone!!
"one" of the reasons I am not putting my coach (1976 Superior Cadillac) in the county parade today is that I suspect the rear end may be low on gear oil (and I have not had the time to get it out and put up on ramps to check yet), just a logical assumption because I have seen a spot on the wooden floor below where the rear end would be sitting and the fact that when I had it at a shop the other week and I was able to walk under the car I noticed that the rear driveshaft was very warm and I could see a small bit of what I think is gear oil at the bottom of both rear brake drums.
I am sure more work will be needed sometime soon, but for now exactly what gear oil do I use to top off the rear end?? I searched this forum a little and got a little confused after reading Jeremy's post from late last year (I don't know how to link a thread??) As far as I know this coach has a positraction rear end, did ALL coaches of this year have the SAME rear end??
Can I just buy the correct gear oil at the parts store?? or do I need to buy gear oil and mix it with something?? and why???

thanks everyone!!
Dana.

I do not know myself what gear oil to run, but if it looks wet at the bottom of both brake drums, I would suspect that as being leaky wheel cylinders. I would check the brakes out. Gear oil and brake fluid would be easily told apart by smell and look.

You very well may be leaking gear oil at the rear pot/driveshaft, but check to make sure your wheel cylinders haven't gone.

Dana, I believe all CC were the same and had posi-traction. You can use gear oil and a separate additive or find gear oil that already has it in it. If you are low I would be more concerned about getting some gear oil in there if you don't have the additive on hand.

My memory of this is a little hazy, but in 1986 I attended my first PCS National meet in Tulsa, OK. I drove my '75 M-M Criterion almost 1100 miles south from Winnipeg, Manitoba, Canada for the event. During the course of the trip, I noted a vibration and noise from the rear end when I was making tight turns. With the assistance of Steve Loftin, I was put in touch with a mechanic with years of experience on these cars. It turns out that this car had posi-traction, and the gear lube that was in it was not correct. We got it changed before I headed home, and had no problems for the rest of the time I had that car.