I had one on an
external door fail fairly recently locking me out for a while. The
square hole central casting had split in two making it impossible to
retract the catch without some cunning and a very large screwdriver.

Luckily I had tools in the garage to take it apart and let myself in.


I have had the same. A nasty casting that often powders away, leaving a
deposit in the cavity.

I bought new handles "sets" complete with shafts, latch and striker plates.
Very inexpensive on Ebay.