Door lock cylinders, what holds them in?

My passenger door lock fell into the door while I was washing my 456GT today. The cylinder is screwed to a mounting plate and that plate was glued to the door skin. That can't be right... right? I can't figure out from the parts diagram if there is something to hold it in place, and my driver's door is the same way.
Anyone know how the lock cylinder is held in place?

 

FYI, this is what the lock cylinder looks like from the inside. No way that's factory, but I have no idea what's missing.

 

Thanks.
Welding after paint doesn't sound like a good idea to me, there's also a tack welded cover plate that makes working in the area tight.
Even with an adhesive, getting that plate in and lined up is going to be tough.

 

I just stripped the plates and cleaned the inside of the door skin. These definitely were never welded. Something is missing.