[byootox]

Just a quick update on this for any others that might go down the same road and want to know the difference.
I picked up the modified dipstick tube yesterday and it's wider at the top to take the different style dipstick with the twin seals.
The seal on my old one was hard and the dipstick was pretty loose.
CNG.. I done the breather system a couple of years ago on it more as a precautionary measure than anything else, it wasn't choked at the time and the ports in the block were clear st that time.
It only does it if I have the car at daft speeds and rpm, otherwise it's fine.
The glove test showed negative pressure at the cap at idle up to about 2000 rpm (car static) and the ptc opening was perfectly clear.
Admittedly a fair bit can happen in 3 years to an engine and the breather check at idle doesn't mean it's perfect higher up the rev range.
The car was mapped about three years ago so the boost pressure will be higher than stock and the crankcase will have a higher positive pressure at the high rpms.
Quite normal for a forced induction factory engine to have a little pressure in the crank case when working hard.