Sure grip?

Hey fellas,

Long time no talk. I have a quadary for ya'll.

I took the 74 into the shop, and one of the techs on my report said the rear differential fluid needed servicing (what I take to mean being replaced). Since this is a relatively simple task, I'm up for doing it myself.

However, as I have read on a bunch of other threads, you guys make mentioning of sure grip. What is it and is there any way to tell if my car might have it?

Any recommendations on gear fluid is also highly appreciated. Car needs another ~$1800 worth of repairs, so anything I can do by myself is a very good thing.

Thanks,

Rick