I have just purchased a 1999 Ski-doo MXZ 600. The sled runs fine, but only has 100 pounds compression exactly on both sides. The past owner has told me he had just changed a piston due to low jetting. You guys have any ideas where it should be and what I should check? Also, a few head botls were leaking antifreze...you think the gaskets are shot? He did not change them he tells me. The sled has only 1300 miles.