Okay,  this subject has been beaten to death out in the world of blogs, but I am hoping for a straight forward answer. On the G503 site, when this is discussed, it turns into a heated battle.  Not about the seals, but who knows stuff and who doesn't.

I interpret what I have read that there are GOOD and BAD rubber seals and GOOD and BAD rope seals out there for sale to unsuspecting Willys folks. And what really stinks is the manufacturers like Felpro and Victor don't seem to take responsibility for poor products.  

I also understand that a perfectly good seal may not seal if machining tolerences are off or pitting exists.
I went into Advanced Auto Parts and they have access to the Felpro rope seal, but it excludes the Military engine.

Again, just after a straight answer if one exists.  I have a 1949 CJ3A, #36662.  Somewhere in its life it got a new Feb 1, 1945 GPW motor. (Most likely a surplus engine. All serial #s have been ground off except the casting information)  It is attached to clean T90 and T18 transmission and transfer cases.

Questions:
1. Would this engine have been originally supplied with the rope seals? And if so, why would Felpro exclude their available rope seal from working in a military motor?  

2. If I am able to find a GOOD seal,  is the rope seal or the rubber seal a better choice for this motor?

3.  And in your opinions, where is the best place to get GOOD rope or GOOD rubber seals and avoid getting the BAD stuff?

I reread your questions, Yes, go with a rope seal, properly installed. If you can find the old stock ones instead of this new replacement stuff they are trying to pass off as a rope seal you will have better luck. The GPW would have originally used a rope seal..

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”.

I used a rope seal (the second time) in mine.  It leaks about a drop the size of your little fingernail every 2 or 3 days.  I can live with that.  Finding a NOS rope seal will be difficult.  They had a bit of asbestos in them apparently.  I have been told that the rope seal from a 302 V8 Ford is a better seal than the rope seal for the L134, and will fit, but I did not use it.  A neoprene seal is suppose to be ok if your crank mikes to 2.30 or less.  "You pays your money, and you takes your chances!".  Jim

Hey athawk11,

I have a friend of mine that has a lot of NOS. I asked him if he had NOS rope seals and he said he is pretty sure. You can contact him at: 
903-268-7260 His name is Ron. I purchased about 90% of my NOS items for my 53 Willys wagon from Ron. He is located in Greenville, TX. Ron does not have a web site, sorry.
Hope he can help you - I told him I would give his number to you. It's worth a call.....Good luck.

George

Hey all,

Good thoughts all around.  George, I'll give Ron from Texas a call.  I bought a seal from Walcks.  It is a neoprene seal, but is not marked with a name brand or part number like some others I have seen.  I want to have both types of seals when I take this thing apart.  As suggested by many who responded,  it makes sense to replace the seal with the the type that is currently in the motor.

Wish me luck.

Tim