Hey guys I know this question has probably been asked a lot, but I am doing an oil change and I live in the North East but only use my tractor 3 or 4 times in the winter to clear snow on a property that I have. have been using 15w40 kubota oil should I use there 10w30 in the winter or leave well enough alone and continue with the 15w40.Machine has 100 hrs on it now.All fluids and filters were changed at the 50 hr mark as stated in manual.And should I stay with there oil or go to synthetic oil like rotella t6.Thank you in advance.