Dang Knifemaker, where you been?
This has been hashed, rehashed, and hashed some more many times over. You can get that Yammie special whale **** from FJRGoodies (Sunnyside) or Gary McCoy for about $18 a bottle IIRC. It's supposed to contain some special anti-foaming agent for "high speed operation", which most think = autobahn, and not needed here in the U.S..
Many use the gear oil of their choice, Mobil1 75-90 synthetic being a popular choice. I have been using the Mobil1, but recently ordered the Yammie special whale **** from Gary McCoy since I was ordering other stuff too. Will be doing a lot of high speed riding this summer, and figured it can't hurt. Now I actually follow the recommended change interval which is like 16,000 miles IIRC, so I ain't changing it that often and it is not a big expense in the great scheme of things. Especially now that tank fill-ups are $15-$18.
