SUCCESS vs Trouble finding rear seal for Duster transmission

I pulled the rear seal out of my 3 speed manual today (71 Duster w 318) and went to two auto parts stores and left with a seal that doesn't fit. What is the best way to find a seal that fits? Depending on how I count, the shaft has 25 splines with a gap that would be space for a 26th spline. Auto Zone and Advanced Auto Parts didn't come up with a match. One of them sent me home with a seal that might have fit into the transmission, but the inner seal was too small for the shaft that needs to go thru it. I've measured the shaft and the seal diameters. Is there a good source where, based on the diminsions I have, I can track down the part online or would I be better off letting one of the parts stores try a bit harder?


Tried another store today and, after the person helping me was ready to order the part - I asked that he verify the dimensions first. That check revealed that it was the wrong part. After more searching online, he looked at my part and found a number stamped in a hard to see place - but HE FOUND THE PART NUMBER. He located the part and it should be at the store in a couple of hours.

Lessons Learned -1) the part number is stamped on the inside where it is really hard to see. 2) There are a lot of seals out there for the 1971 3 speed transmission that don't fit. 3) When you drill a hole in the seal to help with pulling it out - stop drilling after the first layer is penetrated. (I hope I didn't screw something up behind the seal. The peice of metal behind looks okay).

Thanks to all who helped.