Taking seats apart is pretty straighforward. It involves puncturing your fingers on sharp metal and subsequent cursing. Usually. Ok, it's not that hard. 4 bolts to pull your seat and a little prying, a little twistign of hog rings to get into the upholstery. You shouldn't need to get into the back adjusting knobs for what you need to do.
What you're going to want to do is visit the junkyards, and scope out decent passenger seats. The seat heater pad is the same, and of course that seat gets less wear. Some yards will not split up an interior no matter what, so ask first. You may have to buy a whole seat in a different color. Good practice. The heater pads just lay in the top of the foam- if the seat is trashed already you could just cut away the upholstery. Try to pull all the wires out when you take it, or at least cut them as long as possible. With luck you'll find good ones that don't have broken elements.

Or, you can buy replacements from IPD (or Volvo, if you're rich).
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Rob Bareiss, New London CT ::: 86 244DL, 87 244DL, 88 744GLE, 91 244: 808K total