Replace those loose leaky low quality Orings with tighter oversize Viton orings that stay tight and don't lose their tension.  The large sump plug Oring incorperates an aluminum outer ring that allows just the right amount of crush on the inner Oring - no more leaks.  The tranny kick start Oring is oversize and must be forced into place - giving you an oil tight seal that lasts and lasts.  Same with the tranny shift shaft, the tranny cam plate shaft and the tranny shift pawl shaft.  These items along with the silicone gaskets and reed valve breather will give you an oil tight Norton.

This shape is taken from the world famous Harley XR 750 flat tracker. The exhaust port floor is raised for increased velocity and flow in exacuating spent gasses and allowing for a fuller intake charge. Made of steel. An easy drop in kit - simply align with valve guide and slide into place (more info).