Fix for sticky tailgate latch?

[Oberon67]

Hi all. Due to what I assume is internal rust, the tailgate latch on my '81 C10 opens just fine, but the springs won't pull the bolts closed again. I can get them to return to the at-rest position by popping the latch screws out and pulling on the latch assembly with a flat bar; the bolts pop out with a BANG and after that the tailgate is good for exactly one (1) latching and opening cycle, and after that it's stuck open again.

I have sprayed PB Blaster, WD-40 and white lithium grease everywhere I can get access to a mechanical part in this tailgate assembly. I doubt I'm the first person to have this problem.

What's the fix?