Hello, I had a friend ( a real mechanic)help me a year ago replace all the seals in the rear end of my 56 3100 because the Pinion seal leaked and also one of the axle seals. For the yoke & pinion, things didn't fit back the same and we had to make about a 1/8' spacer to fit between the crush sleeve and the yoke end so that the yoke didn't rub on seal flange. It has continued to leak and now I'm determined to fix it. I wish I had the original seal because I think it was different from what we got from Oreillys. Looking at one of the classic parts web sites they show two types of rear seals. The 1/2 ton has a Flange, and the 3/4 ton looks like a flush fit. I'm thinking I need the flush fit seal instead of the flange. That is about the 1/8" difference for the shim we had to make. So any history on seal type and variation would be apreciated. I'm not sure this is the original rearend because there are spots where they have had brackets cut off on the axel shaft. The numbers are 3707340, and D1 which from some other post here seems to be 1/2 ton. The date code is AF 1226, can someone decode that? I'm sure it is a 3.90 ratio. Would the 3/4 & 1/2 ton seals have the same Outside Diameter? Also do they make a sleeve to fix seal wear on my yoke? Thanks for any info or suggestions!