There is a rubber seal that fits over the housing. What I do is put the rubber seal over the housing first and slide it towards the rear. Then take the cover, line it up and snap it into place. Do not try to put the rubber seal inside the cover and then put it on...won't work that way. You will have to give it a nice push near each tab that holds it into place (should be 3 of them, at least on my machine).