I often do it when I am changing plugs...with them out...I just hold the blade open and spray the entire can in there at all the angles I can manage..then I spin the engine over to spit out the bulk of it before putting the new plugs in there....I really don't think any oil that might be left is a problem and, as Keith said, I am more concerned with where it came from. I think the pvc leakage is pretty common.