This fix kinda works for me with some additional mods and My 360 was well knackered
My 360 was about 6 months old and had been working perfectly until one day I came to switch it on after it had been sat idle for a couple of weeks and was greeted with the 3 red lights of death. I had the extreme vrs 1 firmware on it it so no chance of a warranty repair.
After reflashing the firmware (made no difference) I found if I put firm pressure on my southbridge chip it would, and allowing it to heat for 30 secs I could normally restart the 360 and it would continue to work. This worked for a couple of weeks but it got less and less reliable.
I had a look on the net for a popper solution and found a professional console repair company not far from me who fixed 360 among other things. After a week in their care and some fixing I got it back and it worked I fitted it with an intercooler and it continued to work for about a month before it died again.
So back to the pros who did some more fixing, this time when it came back it worked for all of 2 days before failing. After a 3rd visit to the repair shop they declared it was a gonner.
I went back to my original fix I then found i could get the console to run if i pressed down on the motherboard below the dvd drive by the left edge of the gpu heatsink, then i used a plastic peg stuck to the bottom of the dvd to apply pressure as the top of the case got screwed down. This worked for about a week before I was back to the ROD

I then tried adding a heatsink and clamp through the bottom chassis to pull the board down, but this didn't work and I then tried the the x clamp vix and variants of to apply force in various ways but this didn't work either.
So then it was tossed in a cupboard in bits and stayed there for a few months. I hadn't tried the heatgun fix, as it again seemed temporary at best and there was the possibility that it could just as easily destroy the 360 as it could fix it.
Then I stumbled on this and thought well I've tried practically every other fix in the book may as well give this a go.
I added 4mm blocks of eraser to the 4 lower ram chips and screwed it all down. Then switched it on no joy. Added the top case and left it to warm for 20 odd minutes. Still dead.
However the 360 wasn't warming up a lot I could still easily touch the CPU and GPU heatsinks. So then I wrapped it a towel, after half an hour I tried again but still dead, so I wrapped it back up and let it bake for another half hour.
After all this it still didn't work and I was ready to call it quits, but I then thought I'd put some pressure on the GPU heatsink, pressing down forcibly on the left side. Rebooted the 360 and it worked!!
I've added another larger 25x50x4mm block of rubber under the DVD drive to put constant pressure on the left side of the GPU heatsink when the top case is screwed on, (the rubber is placed to the right of the lefthand side heatsink pegs).
And now its working perfectly. Ran it for about 8 hours yesterday with no glitches, let it cool overnight and it's been running off and on today for at least another 4 hours and counting.
I have yet to see if it's a long term fix. I had given up with it to the point where I'd just ordered a brand new 360, it'll be typical if this old one keeps running now!!!
I guess the blocks underneath are holding the board up casing it to flex less now when I add pressure to the GPU heatsink its closing the broken connection.