Does anyone know where to find a replacement spring for the push switches in an AU-717. I'm referring to the springs that are mounted perpendicularly to the switches themselves that allow one button to move out when the other is pushed in. I bought a really dirty AU-710 that is missing one of these springs. I've tried a ball point pen spring, but it's just too strong. The picture below shows where the springs are. I drew in red where the missing spring in my switch is.