Ive dismantled the PCV valve and cleaned and checked it. Al there is inside is a rubber diaphragm and a spring, which were both fine.
Breathers cleaned, although they werent blocked. but a bit dirty.
After soaking the cylinders in ATF last night it pumped lots of blue smoke out the exhaust this morning as it burnt it off. Im pretty sure the exhaust is all clear.
ATF soak could have freed up stuck rings, but I will have to fix the latest leak before I find out.
Using a catch tank (if it works) is a last resort option, which I will go with if I cant fix the problem.
I could run it like that until MOT time at the end of the year.
I did run it with the dipstick lifted an inch or so yesterday in the hope that might prevent another leak appearing, but one appeared anyway.
Not completely convinced that excess crankcase pressure is the problem, but at the same time, struggling to come up with an alternative answer.