Okay! Removed the cover!
After the base plate was off, I soaked it in scalding hot water for several minutes then used a home made tool to open the cap using two lugs I found inside the cap.
See attached images.
I made the tool from a piece of 5/8" by 1/8" aluminum bar stock. Used a grinder to create a tip 7/16" wide and shaved the thickness down to a wedge.
I was able to apply enough force to the part to open it without much trouble at all. It only took me about a minute once the tool was made.
P.S. - Don't forget! When you are working from the "wrong" side of the part the threads appear to run backwards from the normal way! Where you turn the cap counter-clockwise to loosen it from the normal perspective, you now need to turn it clockwise when working from the reversed (inside the camera) perspective.
Thanks for all your help!
Now, I'll dust the camera out with some canned air and I should be back in business!