[patrickt]

Not long ago I searched the Dana/Spicer site to see if I could find any tests or studies that compared the two types of U-joints for strength. While there is loose anecdotal evidence that non-greasable U-joints are stronger, there were no definitive papers to be found. The inconvenience of greasing axle U-joints is pretty minor (IMO), so strength and fit are really the big issues. I don't know if the non-greasable U-joints are exactly the same size or not as the OEM ones. FWIW, my outboard-braked rear from ERA with their custom half-shafts all have greasable U-joints; that's true for the driveshaft as well. I would think that if the non-greasable U-joints had a significant advantage they would probably have gone with them -- but I don't know.