I may not have gotten that deep. Here's what I did:
Undo the strip clip where the ass meets the back, carefully slip everything up like your girlfreinds shirt... if she had velcro on her boobs.
You can see my heater pads and the side bolsters; the bolster on the right is a different shape and density. Weird:
PS, I did re-glue the velcro.
Looking at the heating pad, see the small burn marks:
Looking at the underside of the leather, you see more burns. This damn thing got hot!
So, from what evidence there is, the heating element had some hot points in it, some points of higher resistance, which got much hotter than they should have. This heat caused the foam to shrink. I can't imagine some one sitting in the seat when it got this hot.
I got some foam and spray-glued it to the side bolster and went after it with a knife. I carved it back into the shape that it "kinda should be".
I didn't nail it, I think I needed another layer of foam to get it aesthetically correct. BUT, most importantly, my back doesn't care. The seat feels like it should now, no lump in my left side.