Hi,
I looked at this video, at 9:10 he is showing the retainer and oil seal for the upper shaft. The side with the larger bulge was facing to the rear, or into the transmission. The gasket is on that side of it too.
The side with the bigger bulge has openings for the oil to run down, out of the seal, I guess.
At 11:12 it looks like he has put the retainer and new seal on backwards, the bulged side is facing ahead.
The new retainer and seal that TM Tractor Parts sells has one side more flat than the older seal in his video.
If you put the retainer on backwards, the upper shaft can slide ahead about 1/2", that makes the PTO slip out of engaged, the splines on the PTO clutch are too far from the splines on the rear end of the clutch shaft. Also the seal doesn't seal well facing backwards.
Below is TM Tractor Parts listing with pictures.
Someone also wrote about this in the comments below the video on the Youtube website.
