1987 Cimarron: Remove distributor cap

I have a 1987 Cimarron with a 2.8 liter V6 engine that has a leaking o-ring that goes around the distributor shaft cap that is placed where the distributor used to go since this is a distributor-less engine and I am having difficulty removing this cap due to buildup in crud and varnish and tried a bunch of automotive chemicals already. Earlier on I tried gently tapping on the top of this cap to try to jam it more into place to hopefully stop the leak which did not work but the cap did not have any dent marks from the tapping so I don't think I damaged it from tapping.
Any ideas on how to remove this cap?

vice grips.