OK I opened mine up and cleaned all that paste out, I forgot the stuff between the heatsink and the PCB..... shouldnt matter that much on that side.
Arctic Silver (Silver Oxide thermal paste)
You should NOT use AS5 on a unit like this which has exposed pins and other electronics on the PCB. AS5 is conductive and may cause problems. Additionally, its thermal conductivity is only a 1/10th of what they claim it to be, is 4x less than other competitors and up to 5x more expensive. You can see the
full independent paper here, results on page 8.