I know this post is a few months old, but I recently got the 35 pline deal leak after only 1.5 years and maybe 12k miles. So.. here's what I found from research. Some people say the Dana 60 seal, Spicer 36487, but what I pulled out of mine was a National # 473517. Now, the problem I have is the seals actually wore grooved into my RCV shafts. I was told by RCV and a machine shop to not weld in the grooves and machine them down since they are heat treated shafts. Now RCV said I could machine them down until the grooves are gone, and find another seal that will work.. way too much work in my opinion, but also very pricey to replace the shafts. Okay... now the point of my reply is what I'm considering doing and seeing what everyone thinks. My prorock will not accept a Dana 60 seal due to and adapter that's pressed in to fit that smaller National seal. Not sure why some have it, some dont? The 60 seal has more rubber, more room for flex and deflection. I read on another forum that adapter can be pounded out to fit the 60 seal, but Dynatrac told me they dont recommend it and to put the same seal back in. But I see that seal obviously did not last either, however... there is enough room to fit 2 of them seals back to back if I grind and smooth a small lip on that adapter to meet up with the back stop for the seals. Would anyone recommend that? I will try to add pics to show what I'm talking about. I would think double seal would work great, but I'm no expert, just trying to find a fix for everyone.