Recently I had a customer machine with a heatsink issue. One of the hoops that holds the heatsink in place detached from the motherboard. In the past I've used this method to repair motherboard heatsink issues like this. The only thing I would have done differently is to remove the video card for more room to work.
Motherboard Heatsink Hoop Repair Using Super Glue - No Motherboard Removal or Soldering