Well I started this thread ages ago and really meant to sort out my seat heater in September....best laid plans and all that.
Anyway I decided to have a go this week (as summer actually seems to be over now) and see how do-able a repair would be.
Having got the drivers seat out of the car and into a warm living room (SWMBO out for the day) surprisingly it only took about an hour to fix and now things are toasty again (but not too toasty) just in time for the snow.
I just thought I would post some observations in case it helps anyone. Bear in mind this is a facelift leather seat, the fabric ones seem a lot simpler to get to heating elements.
First off, my seat had a hot spot toward the front left of the seat cushion just inboard of the front to back stitching for the bolster, this is a point where the element across the cushion is soldered and it seems over time the element had flexed where the rigid solder ended and strands broke, increasing the resistance at this point and caused a local hot spot. If you have similar symptoms then a fix could be viable. Instructions for seat removal are in a mtce guide. be sure to disconnect battery and leave for a while before unplugging seat to ensure air bag deactivated.
If your heater does not work at all then, assuming the fault is actually in the seat and not the switch, connectors or supply you will probably have great difficulty finding the break as the element is fixed to the underside of the leather which is then covered by a foam layer and a fabric layer which is stitched into the cover so you need to know where to cut to find the problem. In that situation the good advice from others to look for a replacement seat seems fair
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I found that in my case it wasn't necessary to completely strip the seat or remove all those pesky steel rings because the fault was near the front of the seat cushion so before removing seat I stuck a piece of masking tape on the spot where it got too hot. Then with seat on floor I removed the plastic rake adjusting knob (2 screws), unhitch the plastic trim it sits on (I screw front underneath and couple of push in clips along length. I did not need to completely remove this trim, just release the front so didn't need to remove seat back adjuster etc. Next remove 4 bolts underneath frame to release seat from chassis, motors etc. and you can then get to the lower front edge of the seat cushion. You will need to clip off a few tie wraps holding wiring in place, make a note of positions of cables and ties before you remove them to make sure nothing gets trapped or mis placed when you put it back, I always take a few pics on my phone to remind me
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The bottom edge of the leather cover has a strip of rigid card sown into it which hooks over a lip around the steel seat base. If you compress the cushion, relieving the tension on the edge of the cover it can be unclipped all round and the front can be folded back off the foam to the first row of lateral stitching which in my case was enough to get at the problem. You will find there is a steel ring holding the cover down to a wire in the foam each side which will be in the way, I removed one and had sufficient access.
The inside of the cover has a cloth layer, under this a layer of foam and then the element is stuck to the leather. I made a cut in fabric under point where I had stuck masking tape, then carefully through foam to expose heating wire. The wire zigzags across cushion and (certainly the front element) is soldered where it meets the bolster. Mine had frayed where the rigid solder ended. The element is finely stranded copper based wire. It was a bit blackened and worse for wear at the joint so I cut it back about 3cm, cleaned the wire by gently scraping with craft knife and then I slipped a couple of 6cm lengths of heat shrink tube along the element and crimped it to the soldered end with a small crimp and a ratchet crimper I then ran some solder over join to be sure although I think crimp is sufficient. I then slid the heatshrink tube over the join and shrank it on so wire would not flex as much at the join again. nearly done. I just glued the element back down to the cover, glued the cut edges of the foam together and stitched the fabric covering so it would not pull apart when there was weight on the seat. then just reassemble and hopefully it will be good again. ......
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the aerial lead screen is grounded at the head unit and the amplifier looks as though it is integral with the aerial base on the roof. The screen would only normally be grounded at one end to prevent an eth loop which itself could generate noise but its possible the base unit fixing screw could be providing an eth to screen the electronics so next place is probably to check the mounting is clean and tight. Hopefully you would be able to drop the back edge of the headlining enough to check this out without major strip out although not had to go there myself (yet). 
