Thanks for the suggestions. I'm still trying to get it figured out. I've looked at the diagram I found for what I think is my actual knob, http://www.us.kohler.com/onlinecatal.../1097384_5.pdf
but I'm still not much farther along. The screw in my diagram is actually attached to the handle, can't tell how to get it out.
Redwood, thanks for your link, but that diagram looks like it goes to a control with a handle sticking out, where as mine looks more like the one in the link I put here.