Rear brake pads are dragging a little on my '06 450. The rear wheel spins but not near as freely as my other bikes. I checked the rear wheel bearings and they are fine. I pulled the entire system apart, inspected the caliper piston and seals, replaced the guts in the master cylinder, replaced the pads and pin, replaced the entire rear wheel (brand new rim & spokes) and rotor, and it's still dragging. It appears that the piston in the caliper does not retract as much as it should once I release the lever. It moves about half the distance as my TE610 rear brake. Should I replace the piston and seals in the caliper or buy another caliper?