Got round to picking up my revision R PCV Valve from Hawco, fitted it this morning.
My car still had the original that came with the car. Was fairly manky. Gasket looked good. I'd bought one anyway.
New and old - actually quite a difference in design
Back face of new one.
And pic of it fitted before my engine cover went back on.
Took the car out a drive afterwards. Noticeable difference. Especially nearing full throttle and in higher gears.
Can only guess I was losing some pressure on the old one.