[i4abuygto]

Hello guys,
I took my rear fender flares off my 79 trans am and noticed a rubber gasket type material between the flare and fender on one of them and not the other.
Is this thin rubber necessary as I am going to remount them to the fenders. If it is necessary where would I find it and or what can I use?
The rubber broke apart and is not useable.
Let me know your thoughts.
Thanks