These are good wrecking yard parts.
What happens is, there is this "nub" that sticks out and contacts the rotating parts of the wheel when you have either switch engaged. This nub breaks off from stress, age, whatnot and now you have no cancel.
If you were SUPER skilled you could drill into the end of the plastic, either reinstall your old piece using a small metal piece as a stablizer or just use the metal thingy sticking out as your new "nub".
I just replaced mine with a unit from the wrecking yard. Too easy not to do
Most likely the little black broken off piece comes out too when you disassemble.