Mine's doing it too. The problem appeared two years ago, and it's only on the left bolster, near yer rib cage area. What I've been doing is just running the heater for a while, then turn it off. But yeah, this one little tiny spot gets so hot that it can burn you. Then I noticed that the leather is shrunken and hardened in that area.. which is what leather does when it's exposed to extreme heat.

My theory is that there's a slight fold in the heat pad in that area and it's triggering a micro short in the heater wires in the pad.

So the heater pad is stitched in? Hmm.. I worked with a leather upholstery place when I upgraded my Z3 Roadster's leather seats to Nappa (came out awesome btw)... but I remember working with the seat heater pads. There's two; Seat base and seat back. But they just set 'free' on the seat foam. I'd say, if they're stitched in on an X5 seat, all you need to do is take the car to an upholstery place and have them remove the seat, pull the leather cover, unstitch the pad, replace the pad, and the leather cover. I'll bet they're totally used to having to pull pads and restitch them in place. Upholstery guys are the unsung heros of the car tech world. They gots special skills!