Sliding door lock

Thanks for posting. Remove the handle set from the door and inspect the thumb lever. If it appears damage, then the handle set should be replaced--see the 82-090 or keyed 82-087. You also could just buy the thumb lever, the 82-107, but note it only comes in white. While the handle set is removed, try manually throwing the mortise lock with a slotted screwdriver. If it doesn't budge, then you need a new mortise lock. See if the 82-260 matches up.

Alternate image for 82-260

Alternate view of 82-260