When removing my air box (to do some work on the brake lines) the foam seal/gasket (~6” diameter foam) that seals against the car frame was as brittle as can be. I have removed it but unable to locate a part (as expected). I’m wondering what others may have used as an alternative for this…or maybe someone has located the part…

It would probably be the same as in a 2000-2006 LeSabre, but in those would probably be in similar condition.

As far as making our own, If it were me I'd probably try to make something out of PTFE foam. It supposedly melts at 327 degrees Fahrenheit so it should be good in the cool part of the engine bay. I suppose you could put yours back together with glue then coat it in several layer of some of that flexible spray paint. That'd be an experiment though.

I know others from similar years could be in the same condition, but you could try a salvage yard, and maybe find a decent one.
I use this to search my local yards, you could search for air box, or another part on that vehicle for that matter, once you see what yards have some give them a call, and go see if any have a decent one.

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