Took my 650 to Precision Concepts for a top end. I've got 13K dirt miles on it. Still runs strong, starts easily and runs smooth.....but my intake valves kept tightening up. So PC opened up the top end and recommended valves, piston, springs etc. They believe that the valve damage is due to the UNI Filter passing dirt and highly recommended switching back to the OEM filter. Anyone heard of this?