I've got a left over qt od syn 3 I'll be using in the primary. Stopped a Russmeyers in Daytona and got to talking to a salesman about this and that and oils came up. We both agreed on synthetic in the the motor and a good gear oil in the tranny and when we got to the primary his words were "You could almost pi$$ in the primary" no BS! Almost split my side laughing.

 

I agree that synthetic or indeed anything >$3/qt. in the primary is overkill. I'm using Castrol GTX 20w50 in my '07 SG and it works fine. Moly is great for the engine, but some say it might not be ideal for clutch disks, so I avoid engine oils with high moly levels, like Redline and Royal Purple. I did run Royal Purple 15w40, which has ~250mg moly per quart, in my '96 RK's primary for a while and had no trouble at all--so this may be just another oil myth. Redline MTL has no moly, IIRC, but at $10/qt. is severe overkill IMO. All an oil needs to do there is lube the chain and cool the clutch disks in a very docile environment (unlike engine and tranny), and anything should do that job. I've heard of nearly everything being used in the primary--ATF, engine oil of all types, and gear oil (MTL, etc.). No reports about vegetable oil yet, but I wouldn't go quite that far.

 

I use MTL because it has no moly. Otherwise, I would use Syn3.

 

That is the normal logic used to justify using an in-all-three oil, but when was the last time you had to add oil to either the tranny or primary between changes...?