I have two 2001 XL800, both motors have blown pistons, but don't recall if they were both the rear cylinders. If the rear oil line came off, wouldn't there be a lot of oil in the engine compartment? My main problem has been with power valves - one broke off at the shaft and fell into the cylinder, destroying that piston. Another was completely gone and the last failure was the retaining pin came out and the piston started eating the edge of the power valve. Have R&D billet power valves on order now.