This is just another way to have the suicide door do its evil work--the outer part of the door catch/receiver can fail. Fortunately, this happened on a slow road in Yosemite, so the only door/shell damage was a very slight dent in the skin.
The first photo (1970s model) is the door catch installed and the second photo is the broken casting.
The casting is curious--the side you think should be the strongest only has a bar across the lip, otherwise it's open on that side.
A wooden "wedge" can provide a secondary safety for the door. This design has been documented in several other threads (thanks to BOONDOCKER and all who posted on his recent thread
). The modification I offer here are the ears (there's one on the other side, too) that provide a bit more stability to the wedge (makes it impossible for the wedge to rotate and possibly fall out) and the relief(s) under the tongue that may be necessary, depending on your door trim and fit. I used this wedge for many miles on my Caravel
when the lock jammed--the latch worked but couldn't be locked, which gave me the willies.
This may have been a problem that was previously "fixed" by the PO. Once the receiver casting was removed, I noticed that the door rib was cut away on the exterior side, so the only thing that was keeping the door closed was that narrow bar in the casting. Maybe they had to cut their way in at one time.
I recommend using a piece of solid hardwood for the wedge, not plywood. The tongue is not very thick and I'd be concerned about water-caused delamination in plywood, even if you varnish the heck out of it.