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.

http://www.hondaeasttoledo.net/oempartfinder.htm#/Suzuki_Motor_of_America%2c_Inc/LT250R_(1989)/TRANSMISSION_(MODEL_F%2f%2fG)/01340005/5601340021