Temps slowly creeping up

[Whitebread]

Two years ago I OCed my 165 build to 2.43ghz. At first I was getting temps around 33-34 degrees at idle and around 45 degrees at full load. In the last year or so, idle temps have slowly creeped up to 40 degrees and full load temps have hit 51 degrees on occasion. I keep the case clean and check the fans regularly. What gives? Could the thermistor (or is it a thermocouple?) be going bad or do I need to reseat the heatsink and reapply some thermal grease? Stability doesn't seem to be affected although, I haven't run super-PI since I finished the build so that statement is conjecture's.

Any thoughts?

 

[ring.of.steel]

I say re apply as5 on the cpu.