I have a vectra b gsi aswell as the omega mv6, I fitted metal covers to the omega in the summer this year, I did replace the breather ontop on inlet manifold with brand new, and cleaned the pipes to the breather box. Vectra doesn't suffer with crank seal problems, not sure everyones negativity toward the vectra covers, do you really think vauxhall would spend millions on development to have inherant oil leak problems. Omega covers Do warp, due to the plastic seeing near 100 degrees c, Ive spoken to a few vaux v6 specialists to confirm the warping, I saw it myself after removing them, and having always torqued them correctly, even though they had been removed only once before I replaced. Vauxhall always have stock of the plastic covers, vectra c has plastic covers too, again suffering from leaks, do you honestly think that all owners of platic covers of v6 vauxhalls are incompitent at torqueing up the bolts? Vectra metal covers dont warp as their metal, also the seal is double thickness of omega. They never fill the plugs with oil or allow oil to escape externally. Vauxhall fitted metal covers because of the large inlet manifold so as to support it.
Oil filler ends up next to brake servo, to fill just fit the existing platic filler extension to fill.