You have brought up a topic that has been discussed over and over again here and on every other jeep web site. A simple Google search for Willys L134 rear oil seal will answer your question.
https://www.google.com/?gws_rd=ssl#q=wi ... r+oil+seal
There you can do what most of us did was separate the BS from the facts.
Or just write this down in your copy of the engine manual for your jeep.
1 - There were several years of bad seals produced by Felpro for their own name brand and for others. These were in the 1980/90's. Do not use them!
2 - The early L134's came with cranks that were meant to be used with the rope seal. These did not have the dimensional discipline applied to their sealing journal on the cranks that was applied to the later cranks meant to be used with the formed (lip type) (Garloc type) seals.
3 - When you rebuild the Willys 4 cylinders please read and follow the overhaul manual for the engine. Especially when you have installed the crankshaft with it's bearings and a new rear seal. Before installing rods and pistons the crank should turn easily with your hand on the ends of the crank. If it does not resolve the issue then.
Finally, as with most questions asked here I have provided most of the answers in the hundreds of technical photos in my photo album. It is the 2nd album in the Member's Album page.
http://www.willysmjeeps.com/v2/modules. ... php&page=1
Especially this sub-album dedicated entirely to the issue you have re-opened.
http://www.willysmjeeps.com/v2/modules. ... _album.php
Also make sure your machinist properly cleans up the journal on the crank that the rear seals ride on.
This journal will never allow either type seal to seal well.
