HP Compaq NC4010 Maintenance And Service Manual page 115

Removal and Replacement Procedures
Each time the heat sink is removed, any thermal grease residue
should be carefully cleaned from the heat sink 1 and processor
surfaces 2, and new thermal grease should be applied to both
surfaces.
Removing the Thermal Grease From the Heat Sink and Processor
Reverse the above procedure to install the heat sink.
Maintenance and Service Guide 5–35