When my plastic lever failed, upon removal it looked intact. However, applying slight pressure to it revealed a small crack, enough to allow the lever to bend instead of actuating the safety switch.

A failed brake pedal switch is also a common fault.

 

It is not too unusual to have a hard-to-see crack in the plastic piece that causes intermittent failure. Total failure will be near...

The problem could also be electrical (poor connection causing intermittent failure of the solenoid) or lack of lubrication.