I thought that HD does not recommend the use of GL-5 rated gear oils for the trans., such as the mobil, valvoline, castrol, etc....hypoid oils you guys are using. I heard that because HD trans. primary fluid and the syn 3 stuff is rated to only a GL-1 which is supposed to lubricate the bearings in the tranny somewhat better, and therfore extend life. Now don't get me wrong, not promoting here but, just hearing different opinions that GL-5 rated fluids will not protect the bearings as well.