diff on 872gp

Thought I would see what people thought of this situation and ask some questions. Story. I owner/operate a 872gp. The diff locks stopped working, brought it into dealer. They rebuilt the diff, did new breaks,seals and any parts that needed to be changed, no sense being cheap when your in there. About 10 hrs or so after getting it back the breaks started to make a slight sound. Didn't think so much of it. Wasn't horrible. Now about 200 hrs and two months later, the diff locks fails again. I bring it back into the dealer. They tare the diff apart again, and say the stub shaft had broke, due to load shock. And the reason the breaks made noise is that metal from the stub shaft had gotten into the breaks. I have a strange feeling no one wants to warrenty that. I've been owner operater for 10 years, never have done damage to my diff before in my last 3 graders. All deere. My questions. Can the stub shaft not be installed properly? On the first go around. Ie, mesh of the spines. What kind of force would it take to break the stub shaft? I've never had one break before, and definitey would remember breaking it, that's if it takes a great force to break it. Not just normal blading. Thanks for the help. I must say I love my deere graders, just this diff is confusing me.