Hi Bob
These seals have come up before on MLU you might try a search to see some of the previous comments.
http://www.mapleleafup.org/forums/sh...rear+axle+seal
Having said that I've have never found a modern replacement for this seal though some more recent GM military equipment use a similar seal, different size. The purpose of this seal is to keep the rear end grease from running out into the brake and to prevent water from entering the axle housing when deep water fording. I've run my Pattern 13 C60S with out these seals since 1990 and have never had a problem. Of course I don't operate the truck on extreme side hill slopes anything up to about 10 degrees with no problem. I've even taken the truck further than that when it was stuck in a ditch with out problems. If you do leave these seals out you want to be sure to use a tab locking washer between the nuts to keep them from backing off.