Hi,
I had the drivers side fail a few months ago and replaced under warranty. I chatted to the dealer about the comments on this being a weak area of the vehicle. He said it was about the way the heater sits under the seat area and with movement breaks it, probably the same wire mentioned in the other post.

This probably means that lifespan is not so much through use of the heater , but a combination of miles driven, weight of person and how rough the roads are I'm sure someone mathematical can work out an equation for that .. any takers ?

cheers

Paul