Be careful my NAPA couldn't order the Vinton double lipped seal. One of the other threads warns about using what NAPA says is the correct seal.
I followed David Neibert's instructions and found a bearing place. THANKS DAVE FOR SAVING ME SOME MONEY!!!! I ordered the Chicago Rawhide# 7968 and they said they could get it. I told them it had to be a Vinton double lipped oil seal. Well they got off the phone and cross referenced it to another brand found on the web (TCM) and took the one at the top of the list. Chicago Rawhide# 7967 the single lipped seal. The single lipped one was $4.33 and the double lipped was 8 something. Well I couldn't wait and installed the single lipped one. The outer seal was for dust and I don't plan on driving on gravel, so it will be just fine. That is what some of the guys on the web sell anyhow.
The install is really easy, find the thread where gldiii posts the instructions for replacement. I also sucked out all of the fluid and did a full flush of sc fluid and replaced the seal in about 1 hour. Just take your time and the factory seal has 2 layers of metal, you only need to drill through the first layer to get your screw to thread. SC fluid is $18 at ford for 4 oz. and $6 at GM. Good luck, you won't regret this easy fix.
Michael