Hi everyone!

I very much appreciate all of the advice in advance!

I have a 1989 XT600 kick start version with 37,000 miles on the clock. This is unreal for any bike! Motor has never been opened up.. unreal.. owner changed the oil every 2K miles, was very easy on the bike and never took it off road. Bike has great compression and runs like a clock... starts easy and has plenty of power... I would say that this bike is MUCH more reliable than the Honda Xl600 ...

The main work I did to the engine was to replace the left/right case gaskets as they were seeping... I also had to helicoil the oil filter cover screw as it was strpped... the engine was VERY clean inside from all the oil changes. No signs of any 5th gear chips or particles. I also changed the carb insulators, and all new oil seals.

Main issue I have is I have oil leaking out of the main shaft seal only at high RPM 75 MPH or more riding. if I just keep it in city streets no leaks. I did put in a new seal and it was leaking... thinking the new seal was bad.. I have had this happen in the past.... I put in another new seal... same thing leaking. Oil is all over the tire and runs down the swing arm.

Any ideas out there? I have never seen this happen and I have owned over 140 bikes in my days. I made sure the seal was installed level and flush with the case.

By the way.... the YSS shock for the XT600 is just FANTASTIC!!!! SO HAPPY with the performance... on a fast trail ride the control is just amazing. I also modified the front forks by welding 2 out of the 4 holes in the dampening rod shut. Then you add the progressive springs and you are set... no bottoming with about 5 lbs of air in each fork.

Thanks for the help!!!