, if you are talking about the 14"/14" roof vent, and they just crumbled, I would replace them all, but if you are on a tight budget, you can just replace the cover! The cover screws on along the hinge. I replaced mine with Fantastic Fan's, and the job was very easy, and most have the 12 volt wire already up there in the opening! When done, and everything is sealed up on top with enternabond , you will be glad you swapped them out! Hopes this helps you! Rail!
Retired, and "Always on Holiday!"
1996 Monaco Windsor 38' "Mona"