Old_Blue, looking at the pic of the fractured sear you posted, I can be pretty certain that your problem was not caused by dry firing. That part was defective, for whatever reason. I would hazard a guess that any breakage caused by dry firing would be related to the floating firing pin or spring, not the other internals.
Appreciate the feedback, muddocktor. Anyway, after that talk with customer service, I'm cured of the impression that S&W's 21st-century revolvers are any more able to tolerate dry-firing w/o snap caps than my circa-1990 guns are. Now if they'd just edit their FAQ to make that clear, they might save some money on repairs.