It looks like the cover, although it has a gasket, isn’t designed to be watertight - when washing the car I notice it can be wobbled quite a bit. Looking at the Toyota parts diagram it seems the watertight seal is under the actual antenna block and the cover just snaps onto that block without intended to be watertight. Is that right? I did see a thread where someone said they’d knocked that cover off and they were told water might get into the headliner but I don’t think that’s true.
Yup. Mine rocks, too. When I push it side to side, I see a little gap on the sides. I suppose that what looks like a gasket is really just flexible trim to dress it off. The seal must be inside the cover, but I don't want to play with maybe breaking something just to satisfy my curiosity.
Number of times I’ve done that sort of thing, then something falls off, requires proprietary tool or replacement plastic piece to fix. Next I’ll poke out one of those parking sensor things while testing how firmly they are installed.
