I tokk my 1995 BMW 325i to the shop to have the engine checked. Cylinder 1 is showing low compression. Oil was found to be inside the spark plug.
you have oil coming thru the rings and into the combustion chamber, which will eventually foul that plug. for the short term, you can change that plug as soon as it gets fouled, but the permanent fix is an engine. probably more expensive that the car is worth.
Could also be worn valve guides...