I have a very high mileage(300,000) slightly modified 1.9. Mild cam and webber 32/36. Still retains the stock bore, dished pistons. Had an issue with one of the plastic dipstick plugs being blown(falling?) out of the block. Replaced with a spare, 2 weeks later same thing(a mess!). Replaced with a steel core plug. Got me thinking about pressures, removed large hose from valve cover installed a vac/pressure guage, at idle +1 psi, increased rpm to about 3500 rpm pressure increased to 9 or 10 psi, then dipstick pushed out and all pressure relieved. Could blocking main air intake to valve cover with the guage cause excessive pressure buildup? Ran same test on 89 ford Escort with 139000 miles and a 1.9L motor(PVC system), installed guage at air intake on valve cover, at idle -1vac, increase rpm went to about -4-5 inches of vac. Intresting, I also removed the valve cover on the opel(aluiminum), found the scrubber pads in very bad shape, wonder where all that metal goes, if you have not checked these may want to do that now! I found brass pot scrubbers work very well. I have often wondered why opel used this method of crankase venting/breathing, just about everything else on the road uses a pvc system, I have even seen some water cooled(heated?) pvc systems. Also several designs that use a trap to remove the liquid oil from the vapor and return liquid to the engine and send the vapor to the intake. That vacuume line from the opel valve cover to the intake is so small... seems to me that a proper pvc set up would increase the positive airflow thru the engine, keep crankcase pressures down, help reduce oil leaks and reduce the dirty buildup inside the engine by reducing the ammount of oil vapor condensation. I do suspect I have a pressure problem with my engine, poor ring sealing or piston troubles, runs ok and has the same vaccume readings while running, at idle and down the road. Kind of a long post, hope it makes you go Hmmm.