Zeppelins
Perhaps my memory has failed me again, but there is a priceless letter in FYO from, I'm sure, Hugo Myatt, describing experiments he conducted on engine breathing. He purchased "something for the weekend" - and fitted one of each (they come in packets of three) to the chaincase, the gearbox, and the engine breathers and took the bike out for a dander round the block. If the devices were inflated, then that pointed to the source of the breathing problem. I'm not in a position to check the reference right now, but Hugo Myatt or no, the rider got back to his house with one "device", now the size of a small Zeppelin under his arm, still attached to the engine. There was indeed pressure where there didn't ottabe.
Regardless of whether it was Hugo Myatt or AN Other, it's worth looking up the reference in FYO, both for the amusement it gives, and the insight into Vincent breathing problems. I followed the advice given (the Prof was involved) and it worked. I'd be happy to pass on what I learned and what I did.