smorizio :
think the paste under the cpu dried out or the heat sink not all the way down.
The 'wet' components in thermal paste play little to no role in heat transfer, it is the metal or carbon nanoparticles that provide the bulk of the heat transfer. Liquids/oils/greases are there mainly to turn the solid nanoparticles into a colloidal paste to make them more practical for field application.
The pre-applied paste on Intel HSF is almost completely dry off-the-bat, it is densely packed powder with only as much grease/whatever as required to make it machine-applicable and cohesive enough to stay put on the HSF during shipping and installation. If you try scraping it off even when fresh out of the box, it crumbles and is impossible to stick back on. This stuff would be impossible to squeeze out of a tube or syringe without superhuman strength.
As I said in my post above, the plastic mount and push-pins on Intel's stock HSFs deform over time. When this has progressed to the point of having insufficient mounting pressure, proper mounting is no longer sufficient. Changing the paste may work for a short time but high temperatures will come back. In my case, fresh paste helped for about two weeks and then I went for a 212+.