If the seal, 29 in the picture, is good, try replacing the oring, 36, with a fatter one that has a smaller ID. This causes it to fit tighter around the shaft and seal a little better between the bearing and the spacer.
I had this problem with my 89 250 in 89. After changing the seal and oem oring a couple times and still having a leak, the tighter, fatter oring fixed the problem. It hasn't leaked since.