Engine misfire

I keep getting oil in my coil well rear left side causing a misfire. I have already changed the seal twice not sure how oil is getting tgere ir how to stop it.

Year, make, model?

Make sure the mating surface where the seal seats has no nick or debris (like left over from old seal.
Could also be a warped valve cover.

What car and engine do you have? Which seal has been replaced twice?