I originally put new Bosch Platinum spark plugs in my 1990 Volvo 240. It made my engine run real ruff, so after talking to my Volvo shop mech. he said the 240's do not like the bosch plat. series and to use the other bosch spark plugs(forgot the name). So, after three months of using the Bosch Platinum series spark plugs I switched them out with a diff. bosch series spark plugs. Now my engine runs a lot smooth. But when I switched them out I noticed oil splashed on top of my spark plug wires. I also noticed oil residue running down the top of the engine from the area of the engine cap. My oil level is fine, so it is not a significant quantity. After switching the sparkparks I noticed less oil coming from the cap because there was not oil splashed on top of my wires after driving for a while. But I still think oil is coming from the cap because there seemed to be new fresh oil residue. The engine used to shake hard with the Bosch Platinum spark plugs,could of the shaking made the oil go through the top of the cap? Since the engine is running smoother now with the other spark plugs, what is causing the oil pressure to go upwards through cap since I still have fresh oil residue running down?

 

One of the lines for crank case ventilation may be blocked up. Or you might need a new rubber ring on the cap.

 

I use only NGK plugs and they have no problems. Bosch Platinum are just plain bad plugs that seem to have problems in all kinds of motors. Lately many european brands specify NGK. Your oil problem should not be plug related... oil cap seal +1.