In rebuilding my propeller shafts ('68 CJ5 V6) I discovered that one of the slip yoke seals was rubber and the other was cork...both likely original. The rubber one (rear) actually still had some elasticity, but the cork one (front) fell into pieces with nothing more than a side-ways glance. The rubber one had a part number 2-16-93 and could be found here along with the dust cap... Northern Drivetrain, LLC: Spicer D2K The cork one, not so easily found...and probably not the best idea to use cork again. After some searching, I located the following polyurethane u-cup seals. Likely overkill for a simple dust seal intended to just keep water and dirt separate from the grease, but I don't think I will have to worry about these again in my lifetime. Front: U250-0.875-238B Rear: U250-1.000-250B The O-Ring Store LLC, We make getting O-Rings easy! Good thing about polyurethane seals: They are tough as nails. Bad thing about polyurethane seals: They are tough as nails. Had to get creative to get them up over the larger diameter splines. A long neck funnel paid the ultimate price... End result... A few tips if you go this route: Be sure you have the metal dust cap on first. It would be very tough to get the seal back off in one piece. Cut the funnel neck to fit the rear (larger diameter) shaft first. You can then cut it again to fit the front shaft (smaller diameter). Grease will help it all go smoother and prevent seal damage. Enjoy! Oh, speaking of...that mysterious brown wrapper item included from the o-ring store looked like some kind of lube or something for the seals. Nope, a piece of candy...red label reads, "Enjoy, a piece of handcrafted candy from the Northwest." Alright then.