Did you try to at least remove the dust/dirt which tends to clog those parts over these timespans? With forced air from a pressured can to blow it out, or the other way around with a vacuum cleaner? (But arrest the fan, or unplug it while doing so, if possible! Otherwise it can spin like crazy and working as a generator, even frying the controller!) Furthermore the cooling paste/glue/mat between the die, or the lid of the CPU and the underside of the cooler tends to degrade/dry out, also because of time. Exchanging that requires disassembly, removing the old stuff carefully with isopropanol, reapplying some thermal paste, nothing special, just Arctic MX4 is good enough, and then reattaching the cooler.

Would work wonders, I guess.