I didn't replace it with an OEM piece, but when I did my seat cover swap I went to Jo-Ann fabrics and picked up a piece of foam. Then I cut out a square on the OEM piece and removed all the crumbled foam. Once that was gone I cut a piece of the foam I bought and glued it in to the OEM piece. With a razor and some patience I trimmed it down a bit to form to the original shape. This fixed it and the new seat covers replaced the worn out ones.
"Half the ability to get the job done is not being afraid to try. 90% of the time you wont screw it up any worse then it already is"