The ST switch is a conductive pad that provide a connection across two contacts. It's probably
dirty or tarnished.
I'd also suggest finding another one because of cost.
A word of warning here. If you do decide to take it apart, the same circuit board the contacts
are on is the same board the flash capacitor is soldered to. Because the flash is charged when the
camera is active it holds a charge for a long time. It's about 300V but low power. Ever see the clip
where the dead frog is hit by a current & twitches? I can testify to a very fast reflexive response. Yeow!