Since this gets hidden as a comment, I moved it here.
Get all that dust & junk out of there! Yea!
Use the freeze spray sparingly to lower the temp of a hot part 20F-30F degrees over a few seconds- you can do thermal damage blasting a very hot part with -30C (check the can for actual temp). One part at a time.
I would steer you away from the cork. Silicon Sealer should work well. Give it a few days to cure, it outgasses bad. Working with liquid gasket is hard and messy. I suggest building a gasket using the loose part, a tube of silicon gasket (shower caulk is probably OK even, as long as it is silicon), a very flat surface, and wax paper. Prop the cover up so it does not crush the silicon. Make sure you use the waxy side of the wax paper - the wax stays on the silicon, the paper comes off, and you have a gasket. Clean the wax off before you glue it down or place it on the PC board.
Try to make the new seal the same thickness as the old seal.
If you need an adhesive, use a bit more silicon - it will come off, but it hangs on good, and is impervious to heat up to 1000+F. Press down to make a good seal when you put the cover back and apply pressure for a day (clamp, light weight objects, etc.)
'''How do we find out if the small fan is working? That should be your next step IMHO.'''