Hi Hubie,
How much oil have you in the primary case?
There are different amount shown in various books (mostly too much!!??)
Is yours the earlier type which uses one of the case screws as a level?
Just enough oil(ATF) to cover the bottom chain run is fine
When I built my SR I had a lot of problems with oil leaks from the primary, the new felt ring on the sliding plate was acting as a wick sucking (soaking) the oil up and then draining it out when the bike was stationary????
Eventually I replaced the felt with a cork gasket
I fitted a quad ring between the sliding plate and clutch adptor making a new centre for the plate
The case then needed a breather hole invthe filler cap, been fine for 10 years
HTH
John O R