Right you are of course Grumpy - Compression Release, for easier starting...
Okay, so scratch a Compression Tester as a Christmas present to myself!
Well, not to worry - On with the show...

So I opened the Valve Chest up this morning, and as you can see from the photo below, it's as clean as Kleenex in there:

[Linked Image]

As for the Breather itself, it works perfectly. I blew into the disc-valve opening, and could feel air come out of both of the small liguid return holes at the bottom, as well as the vapour outlet at the top. In order to check the Breather Passage, I then blew into the top of the Oil Filler Tube and could readily feel the air coming out of the Passage where it enters the Valve Chest. Finally, to check the Breather Tube, I removed the Air Cleaner Base, and stuck a Blow Gun into the Carburettor end of the Tube, and was able to feel air entering the Valve Chest at the other end. So the whole Crankcase-ventilation setup appears to be working fine...

Now, as regards compression, I performed the backwards-bounce test as you suggested, and the amount of bounce that resulted seemed quite exemplary. So I'm scratching my head again...(?)

Just by the by, do you happen to know whether this vintage of Quantum is happy to run fully-synthetic oil in it? Some older car engines don't seem to be. I ask because I'm just thinking that some synthetic oil might palpably decrease the amount of vaporisation that is occurring in the crankcase, to the point that even if blow-by was still happening, it might no longer result in the leaks in question...(?)

Well Best Wishes for now,
Mick.