Just recently purchased a 2018 pro s switchback 600 for my wife. She is coming off a 2010 rush 600 pro ride. I have been adding oil in our sleds last few years and have had no troubles with them. I ride a 2011 rush 800 and a 2011 switchback assault 800. Always added about 4oz per tank with ves racing/extreme oil. Should I continue with her sled? All my older sleds smoke a bit and her new one barley at all. Thanks for your time.