The seal was riding here: Those wear marks indicate where the yoke was rubbing up against the bushing. Those weren't there when I installed the prop shaft. I confirmed the extension housing bushing was worn, allowing the main shaft and yoke to move excessively. Unsure if the prop shaft was balanced properly when it was shortened. The local place I took it to for balancing (after swapping in the new yoke) said it looked like it had not been balanced. Additionally, the weights they welded onto it were not tiny. So, perhaps the prop shaft was way out of balance and that is why this happened. I was able to get the transmission out on Thursday, and get the rear housing off, replace the bushing, and get it back together. But, I wasn't able to get the transmission back in the car. Unfortunately, my wrist got injured in a soccer game last night, so I won't be able to get the transmission in for a while.