Let me start by saying I'm an old guy that loves working on anything with a motor to keep himself busy. I recently received 2 Polaris Xplorer 300's with low compression issues. One is a 98 the other a 96. I rebuilt the 98 and bench tested the oil pump. It pumped fine. I put 2 gallons of premix in, and it started and ran fine. After a few runs I disconnected the oil line to the carb and noticed the oil pump was not functioning. Decided it would probably be a premix only machine. I did everything the same on the 96 except this time I noticed the drive shaft on the oil pump (worm gear shaft) was allowed to move in and out close to 3/16 of an inch. When I bench tested the oil pumps the shaft was not allowed to move because of my drive fixture. I took the cover off and the pin that holds the gear from moving in and out was missing. Problem solved. Being old with little to do, I removed the engine on the 98 and the oil pump had the identical issue. I don't have any history on these machines, other than I know they were rebuilt before because of the .020 over piston in each. Can anyone shed any light on how these machines could be 25 years old with that pin missing?