As an owner of a 2012 Leisure Travel Sprinter conversion I have two of the
refrigerator vents (identical top and bottom) on the left outside of the camper.
The rear fixed fastener failed earlier and was replaced by a bent piece of thin
aluminum strap.  Then the latch slip up/down latch failed.
This is my solution to avoiding trying to find a discontinued Dometic LS200 
lower vent and doing the tare required out, paint and install of a new 
replacement vent.

The failure was the latch button on the vent frame broke off of its mount.
The seperation left the mount in place with a hole that had some plastic
reminents form the now gone latch pin.  The residual plastic was carefully
removed and this piece was drawn to fit behind the hole and using something
like JB-Weld to secure it in place.  A 4mm screw was modified by putting a 
4mm pan head screw in a hand drill and applying a file to remove portions of
the screw head to have the size and shape of the latch pin.  Then a nut was 
fitted in this repair part and solvent cemented in place while also attaching
the top part which fits through the remaining hole in the old mount.

The final result is a replacement latch pin that the sliding latch can 
lock onto.

Printed in ABS (so it can be easily solvent cemented) and using two 4mm nuts
one inside this part and one behind the part to lock the screw in place.