I have seen a few that went boom and heard of a few others. I have one in the 8.5" flavor my s10. It will get replaced once I have the money and time to do so because I am not a big fan of the gov-bomb. It acts like an open diff (jack up the back end and you can spin it by hand) and then locks solid after some 1-wheel-peel...that shock loading is what often causes them to throw chunks out the diff cover. My 125hp hasn't managed to blow it up yet...
If you want to know more about them take a look at the patents.
Take a look at the drawings as well as the referenced by and citations.
This one was submitted in 69, approved in 74, and shows the governor (where the gov-lock got its name).
73-up trucks all (with I'm sure a very few exceptions) came with Gov-locks when ordered with the G80 build code. It was the 72 and older trucks that got "Posi" differentials.