1970 and 1971 RPCs include illustration and listing of an oil seal fitted to the crankshaft DS.
No oil seal should be fitted there according to John Healy because those models have a different engine breathing method and fitting the oil seal will result in high pressure in the crankcase.
Britbike.com John Healy's explanation of why not to fit an oil seal to the DS of the crankshaft of 1970 and 1971 model 650's
