The X-clamps are not reused when installing the red ring of death fix kit.

Now that the heat sinks are off both processors, use a plastic spudger to remove all of the old thermal paste residue from the faces of both processors and the inner faces of the heat sinks.

Work slowly as you remove the old residue, as many sensitive components are soldered near the processors. If damaged, you may need a whole new motherboard

It is best to use a solvent such as ArctiClean to dissolve the old thermal paste and remove all residue before applying new paste. Alternatively, you can use a mild solvent such as a high purity rubbing alcohol.

You can also use many classic dry-deoxidating sprays: spray it on the paste then rub it; you will remove the paste almost effortlessly and with no residues.

Now is also a good time to clean any dust out from between the fins of both heat sinks.