I was reading around about transmission oils and I came across this link Does Gear Lube Corrode Yellow Metals probably need to copy and paste but anyways can someone please enlighten me a little further, I see alot of people recommending Spectro 6speed transmission oil and lots of other GL-5 rated oils but the mobil 1 site says its not good to use GL-5 rated oil in harley transmissions due to the corrosion of "yellow metals" like brass and copper..... Is there copper and brass or any other yellow metal in the transmission? I was going to buy mobil 1 75w90 gear oil cuz i heard it was not best to run 20w50 in the tranny, so i am confused I know you can run 20w50 in the tranny but its not the best option. anyways Could someone straighten me out? Oh and if your only reply is look in the oil section or something to that nature please do me a favor and don't reply. Thanks.