Here are a few of my observations and
opinions on rear main seals.

As already mentioned, these old engines are going to leak a bit. When they were designed and built it was normal for an automobile to drip oil. There were wide machining tolerances on the crankshafts and blocks. Rope type rear main seals conform to fit the allotted space so they worked well. During WWII the military realized their vehicles needed to have deep water fording capability for invasions from the sea. One very small part of the new waterproofing included using rubber rear main seals. From what I can tell the rubber seals were first used in production in 1950 on the CJ-V35/U and then continued on with the M38. Both vehicles had permanent built in fording capability. At this time the Civilian Jeeps still used rope type seals. I think this is where the �military vehicle� that is referenced in modern catalogs comes from and is not related to the MB/GPW. With the new rubber seal the tolerances of the crankshaft and block must have been tightened up a bit, but perhaps only on the new military engines. Somewhere in about 1952/53 Willys began to use rubber rear main seals in all 4-cylinder engines, possibly after the end of CJ-3A production. Due to this engine evolution there are a lot of crankshafts with slightly oversize sealing surfaces and lots of blocks with slightly undersize seal areas. Combine these factors with a rubber seal that requires better tolerances, and the installed seal could be too tight. Friction causes heat and the rest can be seen in the failure stories. So even if you have a �good� seal, but it�s installed in a bad location, it could fail. I don�t think you can blame that on Victor or Fel-Pro.
I�d use a rope seal in your GPW engine since that�s what it had originally. Try to get an old stock rope seal since they have proven to be �good�.