Well since these were designed to live behind the mighty SL6, I think you will find it difficult to actually "break" one.
Maybe it will get a little tired, but give up and die, not a chance.
My 904 is from hughes, and I have never even considered cracking one open until reading this thread.
My new garage has a nice big gas heater, and a couple hundred bucks for a good manual, rebuild kit, and an old tired core is cheap for the experience and a little holiday season entertainment...
