Just got a 97 jd GT275 hydrostat with what looks like the k70 or k71 trans.Unknown hours. It takes 4.4 quarts of J20d low vis HY Gard fluid and a changeable filter [27 bucks- yikes].Runs ok but seems a little loud. Has anyone ever put auto-rx in there to clean it out? How long would/did you run it in clean and rinse phase? Anyone switched to synthetic 5w-50 afterwards or instead of Hygard? Thanks for the help.