Redline makes an oil especially for the primary. Supposed to be easy on the stator.

 

You can't go wrong with syn3. The heavy oils are not designed for the primary case. Another post mentioned gear oil sure for a transmission. This is not a MC transmission. It is closer to a automatic car transmission. There are "wet" clutch plates. They are only wet because the oil splashing around in the cse. The oil is to cool and lubricate the chain. How do you think people run open primaries. As the clutch plates do not need oil. Heavy oil will cause the plates to stick together and then you will have lots of problems getting the clutch to engage and disengage so you can shift. neutral will be a total bitc... to find.