There has been a whole lot of serious problems with the rubber type of seals. A rope seal, properly installed, is the way to go with these motors. 

Do a few searches over on the www.g503.com discussion boards for rear main seal failures, you'll see just how bad they were.. Engine lockups and rear main bearing failures were common.

Thanks Bill...

That does not sound good....of course I just found the new and improved neoprene seal at Kaiser-willys and I ordered it...

Whether or not we use it is another matter....

You know I checked g503 for a rubber seal and they only list the rope seal...for good reason maybe....

So Bill, I think you should get a free ride in this future new rebuilt jeep! It worth it!

I will go to the local MVPA show tomorrow and ask around about the seals....

The machinist thinks it will be fine as all the surfaces are machined and clean so it should be a good installation.

I see the shop manual mentions a "lip" seal that was used in later production l-heads..The machinist thinks that the lip seal may have had something to do with the fording/waterproofing.

I will continue to research this...but I'd rather have a few drips on the floor than a seized or damaged engine...can you imagine thinking every time you start it whether or not this will be the day that it blows?

The rubber "lip" seal was first introduced on the military waterproof vehicles and was later factory installed on all the 4 cylinder engines. After reading all the stories and problems I'd say the safe bet is a rope seal. The tolerances of early components (pre rubber seal) may not be up to the requirements for a rubber seal, but the rope will just fit in any size space. If you check the turning torque of the crankshaft with a rubber seal installed you will be fine. Too much torque = friction = heat and problems.