You have not lost it. You never had it. Make sure that the rubber band, which runs around the wide compartment cover is fit all around (push on it, if it's loose).I replaced my cabin filter and I noticed that the filter housing does not have a cover. The only thing that covers it is the wide compartment cover (the one that covers the battery). Did I loose that cover or I never had it. Its an 02 1.8T.