Those lower covers can get warped from the heat down there of from man-handling during removal for, say, a timing belt replacement. Just replace the cover and you'll be fine. Oh, and since you put WD40 on your accessory belts you should just replace them, too, while you're in there. When you get that new lower cover, get the rubber gasket, too. The gasket can get oil-soaked and swell... which might be part of the original problem.