Thank you for the tip. I'll have to keep that one in mind. I got it working again, but I'm a little concerned about how long it will last. There was a bit of a bump in the lower button area that controls speed, incline and start/stop functions. I thought the bump might be causing some unintentional contact on multiple buttons and giving an erroneous control input. I heated the area to see if I could flatten it back out but that didn't do anything. I ended up peeling the front sticker off and exposing the copper button layout underneath, which was also basically a sticker. I figured it was worth a shot to peel that up and flatten out the bump. That seems to have fixed the problem. It must have just got so hot sitting in the sun that the adhesive got soft and the parts didn't all expand the same so the sticker wrinkled when it all cooled down again. I would still be interested in finding a way to replace that touch control with a series of momentary buttons. I was also thinking about ways to replace the whole control panel with an Arduino or similar system. It would remove the preset programs, but I could make new ones.

Maybe that'll be the next step if the controls fail permanently.
Edit to add: So much for that fix! The intermittent fault came back. I can pick a walking speed and start the treadmill, but the 4 mph button doesn't seem to work and others are intermittent. More concerning is that the stop buttons don't work. I can still pull the magnetic safety key to make it stop, but I'd rather have all the buttons working.