Big Problem, Little Info.

[wildcard]

OK, I'm assuming the trans is factory. It's on my 71, 300 I6, 2wd , standard 3 speed.
The rear seal, where the driveshaft bolts on, appears to be leaking. There's oil all under there where the driveshaft has apparently slung it. I put oil in it about 2 weeks ago. And it looks like it has about thrown it all out. I filled it back up today.
When I was putting new U-joints in last summer i noticed it was a little damp. Also it looked like a castle nut holding the yoke in. Is that correct ?
If I take that out, will I be able to remove the seal and how is the best way to remove and reinstall the seal ?
I went to the parts store to get a seal and they said it could be any 1 of 3 that it calls for. And I had no more info on the trans then than I do now. So they sell me one they say is MOST LIKELY to fit.
Any help is appreciated.

[fordman]

yes yo u have to pull the yoke and that nut to get the yoke off to replace the seal. just pry the old seal out and use a socket to driver the new seal in with

there is atrans data tag on the passenger side of the trans. read that tag and take it to the parts place and give it to them to get the right seal.

[wildcard]

OK. Thanks fordman. I always knew you were full of it. Good information that is.