Re: Silver heatsink
As a general rule, thermal paste doesn't wear out. However, it can dry out if subjected to consistently high temps. Ensure that the fan is working and the vents and channels that allow air flow are free from dirt and lint.
You can replace the thermal paste that's already there but make sure to thoroughly clean the existing thermal compound from the top of the cpu and the bottom of the heatsink. When applying the new paste, apply only a small amount to the top of the cpu, more is not better in this case. Don't worry about spreading the paste around, the pressure from the heatsink will do that.