As far as the primary goes no wet clutch manufacture will ever recommend a gear lube coming into contact with their clutches and has additives that could harm the clutch plates of time. That fluid was never designed for clutches. Also the clutch could care less if it is a 40 or 50 weight oil. The oil is only being used to cool the plate material during engagement and disengagement. Now with this said there could be some radical situations where a person might find something that works better, but it isn't meant for continuous street use and certainly not for long service life.
I have read many of your posts on this board in a short period of time, and I respect that you have done your homework on this subject.
To say that no clutch manufacturer will ever recomend gear lube coming into contact with their clutches. Is just plain wrong. How many limited slip applications are there on the road? I work on Tug Boats and we have Rolls Royce thrusters on a Z Drive Tug that has Mobil Gear 629, in the box in a wet clutch application. Several of the other boats that we have use gear oil in conventional clutch/gearbox applications as well. And Some of the older boats use Mobile gear 630. The 630 is as 220wt oil, and the 629 is 150wt industrial gear oil. I don't think it has the hypoid rating however.
So I wouldn't say that no one is reccomending gear oil in a wet clutch application. Now in all fairness yes there are many manufacturers, that recomend hydraulic oil in wet clutch applications. I think this is the same scenario we run into with auto transmission lubes. It all depends on the clutch material. I have another interesting tidbit of info, DTT Transmission Builders up in the NW, are doing a test on a 47RE Dodge Truck transmission running Mobile1 10/30.
Yes there are just about as many oil opinons as there are a$$holes. Some are worth reading, some not. Go to any forum that has a discussion on oil, and you will see a lot of different opinions.
I can say that you are one of the more knowlegable Amsoil guys that I have run accross.
You are correct as I was very narrowly focussing on motorcycle clutches and forgot about the many other applications that you pointed out. I hate to be wrong, but I would rather find this out even if it hurts. Good research. Keep in mind though that an additive of friction modifiers has to be added with gear lube when used in limited slip differentials so clutches won't charter. With wet clutches in motorcycles it is recommended against any oil that has friction modifiers in them. I still would recommend against the practice of using gearlube in the primary though because another job that the fluid has to do is keep the clutch plates clean as well as cool and I don't feel in this application that gearlube would be the best choice.