We haven't had any sort of problem like that. We've run either Porterfield or Carbotech shoes, and are getting a full season of enduros (5-6 1.5 hour races + qual and practices) out of a set of drums before we remove them and have them turned, but have yet to have a complete failure on a drum. All of our drums are O.E. older parts. If you're in a 280, I'm sure the extra weight of the chassis would be harder on various components of your brake system, and if I remember right the rear brakes on a 280 use a different wheel cylinder, and attach a little differently. Maybe it's a bit more efficient than a 240's, and you are getting better braking/generating more heat on of your drums than we are. I know we struggle to get our shoes to wear evenly, with them commonly wearing significantly more on the inner 2/3rds of the crescent.