That is one thing I noticed when I took everything apart.  I had grease inside of the A-arm tubing and on the outside of the pivot tube.  The surface of the bolt is rusty, as well as the inside of the pivot tube.  I think the rust is what caused the bolt to break.  I looked at a new machine and noticed that they went back to the double attachment point for the upper A-arm.  This setup uses two shorter bolts, like the 800 Rangers.