Thanks.

I foolishly thought the boost bottles may have been connected when i was inside typing my first post above (god knows why I'd have done that).

They're definitely independently sealed, which means i have a major leak across the crank centre. I can't get any pressure in either crank case half unless the carb inlet of the opposite cylinder is blocked.

If i spray a spot of crc into the back of the reed cage, then pressure the opposite crank case half, i get instant bubbles showing at the apex of the reed cage. So the air is going straight across the crank centre somehow.

That might make sense if a labyrinth seal was used for the centre bearimg but i came across a thread while searching that suggested the nsr crank centre bearing uses a sprung seal, in which case little or no leakage should be expected.

Oh, and lastly, i found that i needed to seal up the crank oil feed port to be able to generate any pressure while testing. Seems normal enough but it's all new to me, and I've not seen others explicitly mention this in other leak test write discussions.

I'm thinking this means i need to split the cases and expect a replacement/rebuilt crank is on the cards....anyone care to confirm?

Thanks
Scott