poppin spark plug wires

my 1st and 3rd spark plug wires pop up . the 1st one just today popped up and when i went to push it back down i seen there was oil all over the place under the hood. that cylynder has filled with oil before . what causes that? it's happening more and more often. i don't need to get stuck anywhere. but what i have to do is pull the plug wire, wipe all the oil off it , clean down the cylinder etc. every so often the spark plug itself has shimmied out too.

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