[/quote]
This stuff is somewhat new to me - the vis of gear oils versus motor oils, so I apoligize if I'm missing some of the depth of knowledge.
I realize the primary is not a candidate for high tech lubrication, darn near anything will work in there.
The main problems we've seen haven't been parts failures related to the thicker lube. The problem has been ease of shifting, finding neutral, and clutch disengagement. I dont know if it has something to do with some of the particular brands people have tried in there, but every single time that we've put F+, Syn3, MTL, or Light shockproof (in the XL platform) in their place, those issues have disappeared. Heck, we've even had people put the HD360 in there with no problems.
kballowe, which bearing have you heard of problems with in the primary?? I havent seen a single one of these, so Im curious. [/quote]
There are a few threads regarding bearing failures on the HD forums - here's one
Bearing failures
I agree that some fluids seem to provide "better shifting" than others and that the Formula+ does a nice job. And you're right that you can use just about anything in the primary.
In my mind there are cheaper and better fluids for the transmission than the Formula+. However, the proof is in the pudding, so they say. I've seen many 100,000+ mile bikes running nothing but Formula+ in the transmissions. So..... it certainly doesn't harm anything.
I think the point I was trying to make is that while the Formula+ works well for the intended purpose, it is certainly nothing special. But - looking at the virgin oil analysis makes me wonder how they get $6 a quart for the stuff.