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i contacted spectro on 12/23/09 and the vice president of sales rollin karoll from brookfield,ct. 1-800-243-8645 emailed me back and said i could use either the platinum heavy duty 75w140 or the 6 speed gear oil. he further stated he used the 6 speed gear oil in both his bikes.an 87 and 91 fxsts and is very happy with it's performance.he said i could use their synthetic 20w50 hd motor oil in the trans and that it exceeds hd syn-3 but he would recommend using the gear oil."it just makes no sense using motor oil in a transmission application." i choose to use the 6 speed because my 4th gear has always had a different sound to it and the 6 speed oil is suppose to help quiet down trans noise.it was a $1.00 a bottle difference and i figure on running it 10,000 miles between changes for now but results will tell. Motorcycle Parts, Discount Motorcycle Tires, Motorcycle Gear, Motorcycle Accessories | Jake Wilson had the 6 speed for $16.99 and the chaincase oil for $7.99 a quart with free ground shipping.Motocross apparel, mx gear, motocross boots, motorcycle helmets at Bobscycle.com also has it reasonable but did charge for shipping if under $150.00 per order. thanks for the info on mischlers in beaver dam,i am in janesville not too far away..