I took mine out to clean the tips and didn't replace the seals. A few weeks later I started to smell gas on and off. The smell came from under the UIM. When I pulled the injectors again to replace the seals 2 came out too easy - probably the ones that leaked. Replaced both seals on all and the smell is gone. I had to order them from Standard Auto because no one here stocked them. Plan your parts orders because Contour parts are becoming rare.
