1991 Lumina Van APV rear hatch won't lock

I don’t know how the mechanism is supposed to work to lock it. There is an arrow to the left but when I insert the door key it goes in half way and nothing turns. Oddly enough the ignition key goes in all the way but still no action to lock it. Does anyone have any experience with this? I will try some lube in the key hole but mostly I need to know what it is supposed to do. Thanks

I really think that you may have a bad tumbler in the rear hatch. That said, I drove one of those things for 4 years and at one time I could not get into the car at 05:30 with a horrible day waiting for me. The mechanism has a arm that bends and the handles won’t work to open the doors.

Is this something that I can open up and possibly fix? It does open when you turn to the right just no locking function as of yet.