Electrocompaniet EMC-1 and Hot Weather

I learned last night that in hot weather the plexiglass on the front of the Electrocompaniet EMC-1 can expand and press tightly against the control buttons possibly causing them to stick. My previous track button got stuck. This morning all is back to normal. Fortunately, here in the Bay area hot days are rare.
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.
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