Applogies, those of you who corrected me are of course right about the shuttle valve - 2 inlets and 2 outlets, I'm going to plead "senior moment". I look on it as a cul-de-sac in development (the Series appendix?) as it seems to add more failure modes than it removes. Re the "o" rings, so far I've not found any seals that are specials. Its the 1960s and everything seems to be a standard off the shelf part, I doubt there was any money for "specials". They will of course be imperial.

ExMil109 said:

Well, I tried one of these...
and the cap part fits on the master cylinder no problem, but as Blackburn said, there's a baffle inside the m/c that separates the two fluid compartments, and the float tube hits the baffle. So, no joy...

Click to expand...

Yeah, just checked the reservoir of my new master cylinder...and baffle right across the middle of the filler cap. So that's not going to work for me, either (as-is). Shame, as that would have been very neat. Might still get one and experiment with cutting the tube down - I can tolerate the odd false alarm as the fluid sloshes about a bit...as long as the float can drop low enough to trigger.

Thanks for the pointer.