My 1920 W&P engine does indeed have a breather onto the primary drive chain. I'd guess that this would be detrimental on a belt driver tho. My own TT Ariel seems to externally lubricate as well, including liberal coating of any drive friction surfaces, so I'd be interested in the outcome of your investigation. I was always under the impression that it breathed through the mainshaft but maybe I'm getting confused. It don't take much..
Swindon Branch Secretary
Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
The Offroad Fleet - Fantic 200, Bultaco Pursang, Beta Rev 3