In March when I summerized sleds I noticed my wife's 2016 600 Rush Pro S had what I thought to be a lean reading plug on the pto side of the engine. Not white but substantially lighter than the mag side. Can someone suggest a flow sheet on things to check. This sled has about 2,000 miles on it and runs great. It still had the original plugs. I changed them out but am thinking I ought to investigate this further before next winter. I have seen past articles on injectors getting plugged as one possiblity but need to hear from you the experts.