driver's door will not lock

[bullwinkle3331]

Hello Everyone,
Fairly new to the forum and working on a '65 C20 long bed that I have had for a couple of months. I have a problem and need a little direction.

I have an issue with the driver's door that the key will not turn and lock the door. I have sprayed a little lube into the lock itself and nothing. Has anyone run into this issue before and can help with direction to the area that I will need to look at? Wondering if it may be the door latch mechanism itself or the door handle.

Thanks for your help!