OK. This might be a dumb question but how much force can you apply to loosen the spark plug? I have two spark plugs that will loosen about half turn but after that they get stuck. I didn't apply too much force in fear of creating major problem like breaking or stripped something. Other four spark plugs came out pretty easily. I do have a torque wrench so I can set it before loosing so I don't over force the plugs... Any idea? By the way, my car is 1995 525i M50. Thanks in advance for any info...