LX178 transaxle slips when it gets warm. I have read and heard you should not change the oil, would this seem to be a reasonable thing to do to see if it helps? Rather than pay $1300 for a new one I'll try about anything. I really like the tractor other than the transaxle it runs and look great. What do you use for 10W-30 oil since the API ratings in the manual are no longer made?