Just bought a 2006 nytro last weekend.The sled runs great and is in good shape with only 4700 km. The one thing I did not check when I bought it was the coolant. Well tonight I finally got around to checking it and am worried with what I have found. The coolant level in the reservoir is low and its lite brown in colour. I am worried that it is a head gasket issue. The only other thing I can think of is that it hasn't been changed for a very long time, but everything is mostly aluminum on these sleds so would coolant turn brown from age? Any insight would be appreciated.