Yesturday arvo my car (96 vitara efi) developed a bit of a missfire when under load only every now and then so i got new spark plugs and missfire is gone
but looking at the plugs i took out there is oil on the thread and black crap around the top of the threaded bit

but the bit that sparks is sort of white
These plugs are about 15,000 to 20,000 kms old if that helps
Cheers Joe