OK Brian,
I will stand shoulder to shoulder with you on this one.
Fork oils for forks, ATF in the transmission ( read primary) .
Hey, you guys are not going to hurt my feelings with that sentiment ... I could argue that side too! It makes sense.
My usage is based on trial and error and experience. I understand and appreciate the theory, but as the military guys say, The Book gets written by guys who didn't follow The Book.
I like to change as things need changing. For example, on setting the timing for an older bike, I will get it "close" using the book values, then adjust it so that the bike is not "pinging", not overheating, making good power, and set it there, regardless of what the spec says.
I know other guys who religiously set the timing according to the manual. Despite possibly having some carbon in the chamber, despite vastly different fuels and octane ratings than 50 years ago, despite all the other variables of load, altitude etc. - they'll set it by The Book with a micrometer and be happy. Never mind that the bike is pinging and overheating and not making much power, it's at 5/32" BTDC plus or minus a mil and that's what it's supposed to be ....
At any rate, timing, oil, or tires, none of it is the Pelagian Heresy, is it?
Lannis