I don't know about the big bodied car, but Zoonhollis 123 car probably has a broken leaf spring in the latch mechanism. If the big car has the same latch, that's probably the problem with it also.
You can get them anywhere Benz parts are sold. I think it's a safe bet that the parts shop on this site has it and it is reasonably priced.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in