Thanks for those suggestions. I did try to run my knife along the edge but maybe a razor blade is a better tool. But as they say in Maine, "it's tighter than bark to a tree.
RainDog - I'm wondering where you drive the shim. It is least tight for and aft but I still do not have a gap. I played with a screw driver but saw that was going to become a ding and I quit.
I do have a wood toggle that I used as a lever but without success. The wood bowed but did not pop out.
Have any of you ever considered using a penetrating oil to loosen the stuck edges? Or will that make it worse? If I ever get this unstuck, I will sand them for this summer and then sand and varnish them for next year.