After completing this process and reapplying thermal paste on my CPU and GPU, CPU Core 1 & 2 temperature sensors were not being read. As a result, my fan was not operating and the CPU diode temperature jumped to >100C.
To fix this I had to reset the SMC (System Management Controller). For this model it is done by holding done Shift+Control+Option and pressing the power button while the computer is off.
I have OS X 10.8.5 running. I also replaced my battery at the same time as reapplying thermal paste. No idea if that affected the temperature sensors.