Create Source from Executable

Can Source be created from a Executable? In my previous jobs we could do this on a IBM S38 many years ago.

I have a small program that Unicon gave us that is used in Date Routines. Works fine but in case we run into trouble I would like to take look and fix it if possible. I Talked to Masoud from Unicon and he does not have the source either.  Currently on Version 10.3.1. The program is called "50" in case someone has the source.