After my high speed trip back from Gaydon I had noticed some oil leaks from the spark plug side of the engine, it seemed to be coming from the head gasket, not good. However, that side of teh engine doesn't have a reputation for leaking and shouldn't cause a problem. I suspected excessive crank case compression caused by worn rings but this is a "new" engine, probably only 5 thousand miles old. Could it be a blown head gasket? The only think I'd done to the car that could have influenced this was to fit the catch tank. So I investigated, the catch tank inlet is narrower than the rocker box vent that feeds it, could the step down create a restriction that could allow a build up of pressure? I seriously doubt it but I've gone back to vernting to atmosphere for the rocker cover vent. I didn't want the catch tank to sit there doing nowt so I opened up the vent at fuel pump blanking plate (the pumps now electric and in the boot) and vented that to the catch tan...