Electrocompaniet EMC-1 and Hot Weather

My back-track button sticks; I'll try a slightly-simpler scheme: after removing the plexi fascia, I'll use a small piece of rolled-up sandpaper to CONCENTRICALLY ream the circle larger. The springiness of the rolled up sandpaper will cause it to enlarge to the hole's size; ream clockwise or counterclockwise as necessary to provide sufficient friction for reaming, yet without jamming. Will result in a perfectly round hole...easier than a circular file's successive approximation of a true circle, no?
Thanks for the tip on the black marker finish! Ernie

This is a commen problem, I have known it to happen on 4 units. The cure for this is simple. Go to the hardware store and get a circular file. Remove the plexyglass front. Carefully file keeping the hole round a bit at a time. Replace the plexyglass - screw it back in - to see if the buttons are free. When finished fileing, cover the filed area with black magic marker - it won't show.