Look here: Potential fix for J1 clicking and clogging - #3 by nnowak
When you unscrew the heat break from the heat sink, there is a good chance you just see a blank M6 thread just with some minor traces of thermal paste if you are lucky. The thread should be covered in thermal paste to provide a decent heat conduction though.
From my point of view it is however easier to unscrew the fan and PCB from the heat sink instead of unscrewing the temperature sensor and the heater cartridge from the heat block as nnowak did there. But that is personal preference. Just take some photos andd make sure the wires will run in the same way they did prior to disassembly when you screw everything together again.
Regarding thermal paste: yes, a good CPU thermal paste does the job here as well since it is the cold end of the heat break that gets the stuff. I used Arctic MX-4.