differential yoke causes rear trans seal leak?

[68 TT]

I have seen this a bunch of times. You have a 1330 U-joint on your driveshaft sitting in a 1310 pinion yoke on the rear end. Same cap diameters but different center section cross widths.

The tops of the U-joint caps should be inboard of the nibs with the 1310 U-joint pinion yoke like you have.

It seems like it works when you put it together but there is nothing to keep the U-joint centered in the yoke side to side. Just a few thousandths of an inch off center can cause a really bad vibration and damage to the trans like you are seeing.

You can put on a 1330 pinion yoke to use your driveshaft as is or put a cross over 1330 to 1310 U-joint into the driveshaft and leave the rear end alone.

I would get the 1330 pinion yoke so you can stay with the stronger U-joint and use much less expensive U-joints in the future. Cross over joints are typically quite a bit more money and not stocked at many of the parts stores. You usually have to pick one up from their in town depot store. Having the driveshaft modified to use 1310 U-joints is an option as well but you end up with a weaker U-joint out of the deal.