Paste is a good idea, since there is no conductivity issue on the back of the PCB. Is it possible to remove the back side heatsinks without touching the ones on the front? I'm a little hesitant touching those, since I wouldn't know where to get replacement thermal pads with 20W/mK of thermal conductivity and electrical isolation. In the name of right to repair and keeping these things running for as long as possible, I'd really appreciate if you could release more information on the ones you put into the machines.
I regard them as consumables, just like the fan, which you did a great job of documenting.

For what it's worth, I plan to design a 3D-printable shroud for the back of the unit that lets you route the cables out the top and funnels the air further back where a secondary fan will be placed. Interested to see if it makes any difference.

I love how tinker-friendly this device is, not gonna lie!