I ended up replacing the seat heater and it wasn't very complicated, just a bit labour intensive. It took me about 3 hours in total.
I laid out a piece of carpet on my garage floor and got to work. Four bolts to hold the chair to the floor. Once it was unbolted I could unplug the wiring harnesses and then I was able to swing it out of the Jeep and onto the carpet. The seatbelt stays attached however.
The leather seat cover then needs to be removed and that is the tricky part. It is easier if you have long skinny fingers but I managed to get it off. Basically the cover wraps around and hooks onto the bottom of the seat frame. Once that came off I could see how the heater pad connects. My Jeep has ventilated seats as well so affects what type of heating pad I needed.
Basically I pulled the old heater pad off the seatfoam and laid the new one in place. There are plastic ridges in the seat cover that secure the heater pad in place and sort off click in place on the foam cushion.
Once it was all in place put the cover back over the foam and clipped it back into place. Again this was a pain in the butt but I managed to get it all secured in place again. Then put the seat back in, connect the harnesses and bolt it in place. Works like a charm now
This is what the foam looks like with the seat heater pad on it.
The black round thing on the front of the seat frame is the ventilator.