I would carefully remove the seal kit in it's entirety, removing any metal rods and clips that hold it in place. Then spool that up and put it into a 5 gallon pail. Fill the pail with at least 1 cup of bleach, 1/2 cup of baking soda, and some dish soap. Then add hot water enough to cover the gasket so the entire thing is submerged. You may need to put something with a plastic base on top the seal so it doesn't float above water. Then cover and let it sit for a couple of days.
Carefully remove, rinse, and with a tooth brush, baking soda and soap, rinse and wash it.
If you have another dishwasher, you could put the seal in the top rack of that and run it through.
It should come out like new. It may even regain some ply-ability.
Good luck. That thing looks so ..... I've never seen anything like that.