What is my seal called?

Everybody has pretty much got you covered. I will add, when you put the yoke back on put some NON HARDENING thread sealant on the splines before you slide it on. I have seen them leak through the splines after they have been disturbed.

Here is a link for some service manuals:

http://www.forabodiesonly.com/mopar/showthread.php?t=132309&highlight=service+manuals

Open them and save them to your computer. I saved all of them.

thanks very much! Do you mean as in permatex silicone? I have orange, black. A couple different ones. Thanks for the manuals! I truly appreciate that.
I am trying to measure the nut. Looks to be a 1 1/4 inch. Hard to get the ruler on it.