Justin wrote:
Hello,
After locking myself out of my apartment yesterday, I managed to make
the problem worse by fiddling with a piece of plastic in the lock
which broke off and ended up being shoved pretty far into the back of
the key hole. I tried using some needles to get it out, but no dice.
Anyone have a reasonably cheap solution? Would injecting acetone
damage the mechanism in any way?

Not all plastics are soluble in acetone, and I suspect, as others, that
it will gum things up. To dissolve it you would probably need to flush
quite a bit with acetone then you risk harming the paint on the door.