Unusual Thermal Paste

[2X]

Hi,
I removed the below heatsink and it had an unusual thermal paste where was very sticky and very hardly could dissolve with Isopropyl Alcohol. I used zippo (Lighter Fluid) to dissolved and remove it. Can you recognise from the color what kind of thermal paste is? I believe is a kind o thermal paste that don’t need to replaced (like the thermal pastes that used on PC CPUs for instance) until the heatsink is removed. This paste I beleive I have seen it again in Isolated DC/DC Converters.

Random picture of an Isolated DC/DC Converter
https://ae01.alicdn.com/kf/He3c76c1c55ce445a8c6416fb8a5cf2924.jpg_640x640Q90.jpg_.webp

[coromonadalix]

you can find thermal pads with variable thickness,  they start at 0.5mm and up