Defrost door fastener?

[Minuit]

This is on my '91 with A/C. It's the original heater box.

 

There doesn't seem to be any fastener for the defroster door in the HVAC box. If I pull on the shaft that connects it to the vacuum actuator it will come out of its little slot in the box and get stuck. I can't see a spot for for a fastener to go and I can't find any reference to it in the parts manual, but is there something that's supposed to be there? I can provide a pic if necessary.

[HOrnbrod]

I think you are referring to:  Push Nut, J4000369

[Minuit]

From the drawings it looks like there's only push nuts on the "driver" side where the door attaches to the vacuum actuator's shaft. Is there supposed to be one on the other end? The push nut on the driver side of the door is there.

 

Here's a video of what I'm talking about:

 

[HOrnbrod]

I don't know. Never had a problem like that or been in there.   :dunno:

[Ωhm]

0:07 to 0:08, in front of your finger/thumb on the shaft:

Does the shaft diameter increase? If so, shaft may have open the hole (in the case) a little larger allowing the shaft to pull out of the case.  

[Minuit]

0:07 to 0:08, in front of your finger/thumb on the shaft:

Does the shaft diameter increase? If so, shaft may have open the hole (in the case) a little larger allowing the shaft to pull out of the case.  

 

I don't see any change in the diameter.

 

This is really weird. I don't see anywhere there would be a fastener, any signs of a fastener that is missing, or anything broken on the heater box that would prevent this. Once the box is installed it's never caused a problem (it's been this way at least since I replaced my heater core almost 2 years ago) but it's really easy to knock it loose while installing it.