Gasket Material for Kitchen Fan Cover

[bevman]

Hello,
As you can see in the attached photo, the black foam sheet gasket has gotten crisp and loose over the last 50 years.

What should I use to replace this and where should I get it?

[Ganglin]

I'd go with something called pipe saddle gasket. It's black foam about a quarter inch thick and pretty tough stuff. The last I bought came from Lowes in a square I believe 7" x 7" - it should be in the sewer pipe aisle.