Pcv valve
 

Having owning my gf8 since Christmas I've noticed some oil leaks on the bottom of the engine one being the front mains oil seal which I did a few weeks ago .No it looks like the rear mains might need changing but I've been reading that the pcv valve block up and cause pressure blowing the main crank seals how true is this .Its had a clutch fitted not long before I bought her it would seem pretty stupid not to change the seal or the oil separator if it was leaking

Yes they can get clogged with muck and if stuck open, turbo boost can increase the pressure in the crankcase.

http://clarkdh.net23.net/NTL/PCV%20valve1.png

I see lol .Might might sound silly but if I have an oil leak from that area (behind the flywheel) and I change the pcv valve will this reduce the pressure on the rear mains seal or oil separator in theory.Apprently there surposed to be changed every 30 thou.

No idea as you/I don't know if that's the actual problem.

Why not take it out and check that it's clean and functioning or simply replace with new?

https://www.importcarparts.co.uk/par...y=&searchPart=