It's not unheard of here to read of the issue just being time and road-loosened connections on the back of the panel. Beyond checking that, consider taking the panel to an electronics repair shop. A circuit board device, capacitor or resistor, etc, that's less than a dollar may be (probably is) all that needs replacing. And many times I've simply resoldered only-seen-with-a-magnifying-lens micro-cracked solder joints to restore an appliance or other device. Micro- or nano- cracks in solder joints occur especially with devices that heat and cool repeatedly, but bouncing down roads for years doesn't help either.
Joel