I guess I don't know what a plastic spring loaded cover is. There are no springs associated with the locks. If you mean the push/pull tabs at the top of the door to manually lock/unlock the door, then they don't usually break unless someone really torques on them because the lock mechanism is jammed?
I know in the 91's, the power door lock in the passenger door can get rusty and stop operating, preventing the key or the push tab from locking or unlocking.
If the key doesn't work in either door, and it used to work in both doors, and you haven't had a new key made that doesn't work quite right, you'll need to pull the interior door panels and spray lubricant on the lock mechanism, then get some movement by exercising the key, or with a screwdriver to try to manually move the lock and help free it up...good luck...Chris