I don't recall seeing a gasket on my cars for the quarter extension, but have seen some sealer. Also, the factory painted the car with the extensions on the car already so you wouldn't see the break in the body lines so distinctly (the quarter extensions never mate up perfectly with the quarter, and thus draw attention to the mismatch, however small, when not painted with them on the car). My paint and body guy stressed this to me recently. This comment is not to detract in any way at all with the outstanding work going on here. Just a difference in opinion it seems.