I finally tried pushing down very hard on the heat sink. I heard a click and speedfan is reporting temperatures 15F cooler than before. I must have dislodged the heat sink the last time I had to go in and reseat the optical drive cables to the motherboard, something I have to do every month or so.
On the bright side, this has been a learning experience for me about heat sinks, coolant pads, coolant gel, etc.
If I ever do find it cheaper to build my own PC than buy one, I will know what to expect.
__________________
Exercise your rights and remember your obligations - VOTE!
I have always believed that hope is that stubborn thing inside us that insists, despite all the evidence to the contrary, that something better awaits us so long as we have the courage to keep reaching, to keep working, to keep fighting. --
Barack Hussein Obama