Blind rivet issues, and Cleaveland Aircraft Tool excellence!

I use the Surebonder swivel head hand rivet tool supplied by Cleaveland Aircraft Tool for pulling blind rivets, and I've had problems start at about the same point in the service life of the tool. A few hundred rivets into the life of the tool, and it will begin to break the mandrel at the pulling jaws instead of near the mandrel head. Eventually one will break long... then after a few more successful pulls, another will break long... and the failure frequency gradually increases from there. Cleaveland Aircraft Tool really stands behind their sales, and has insisted on sending me a new one when the old one starts failing. I'm on my third tool now, and I've discussed it at length with Annette and Mark. My pulling technique is proper; both tools seemed to be adjusted correctly and disassembly and examination showed no anomalies. I've sent both my old ones back for their examination. What surprises me is that according to Cleaveland, the issue hasn't occurred with the Surebonder tool for any other builders as far as they know; the tool should always work, and shouldn't wear out. We discussed the possibility of a bad batch of mandrels, but that seems unlikely due to the randomness of occurrence, using both CS4-4 and LP4-3 blind rivets. I can also tell, just by the feel of the tool in action, when it is more likely to occur. I'd like to hear from other builders who have had similar experiences, and what may have been learned.

Follow up: My third tool began failing today in the same manner as the previous two. I wrote Cleaveland Tool to let them know; they informed me that because of the quality of the tool, they discontinued carrying the Surebonder rivet tool after my experience. Once again they offered to refund my money and once again I declined; I figured after getting three tools for the price of one and several years of cumulative work, I got my money's worth. They currently are not selling a blind rivet hand pulling tool because they haven't found one that meets their quality standards. For now they are referring their customers to hardware retailers or Amazon. Cleaveland Tool remains one of the most honorable companies I've ever done business with.