My thanks to the suggestions to spray contact cleaner into the pushbutton assemblies -- it worked like a charm. Thanks!

My procedure was to disassemble the timer (there's 4 screws under the feet on the bottom), and spray the cleaner into anyplace on the buttons that looked like it would get inside of the button assemblies (using the long straw that came with the can of cleaner) while working the button with my other hand. I dried the excess cleaner with canned air. I then left the unit overnoght to be sure all of the cleaner was gone (it's flamible). All the buttons now work like new.

A note to others who might need to do this: be a little careful when re-assembling the unit so you do not pinch any of the wires.

An interesting side note: GraLab replied to my question with a "sorry we don't make that anymore" response, and were disappointingly unhelpful.