Git is very easy to install locally and would be helpful in tracking the problematic change(s). Git is also quite easy to extend to allow multiple participant. Once installed the basics are easy enough to pick up and there is an abundance of tutorials and guides. My own anecdote is that I found it tremendously useful for my latest Perl projects even before I started adding other people to the project. I did it early in the first one but realized that it would have been even better to use it from the start.