What to use instead of thermal paste?

The original thermal paste is dissolved by the oil and is replaced by liquid metal that only melts at >95C. He heats the CPU to 98C to apply it (the CPU should never exceed 95C during use, I suppose?).
He used Indigo Xtreme. (Indigo XS has exactly 2x more thermal conductivity in W/mK to perform better).

In short, he solders the base of the heatsink onto the IHS with the minimum thickness possible.
We find a product that is very expensive and difficult to apply (the burn that melts the metal is very hot; better not to mess up, and the metal conducts electricity; better not to mess up). It offers little improvement for basic CPU use compared to pastes, even though it ranks at the top (poor quality/price and ease of use/price ratio).
But the more we push the overclocking, the very low thermal resistance becomes increasingly important, and the gap widens in favor of the metal.

The oil cools his PC very, very slowly, taking dozens of minutes to dissipate the watts.
But it works.
As soon as we have a lot of heat to dissipate very quickly over a small surface, thermal pastes become necessary.

If we increase the heat produced per square centimeter, we move to metal.
Despite the decreasing power consumption of chips with miniaturization and 3D, we are increasing the heat produced per square centimeter of cooling surface.

Water cooling remains superior to air cooling but becomes TIM limited if we stick to classic thermal paste.

Back to square one, metal is not fun.

Oil cools but not swiftly.
At around 95C, we remain in the realm of liquid water without the particular properties of indium close to its melting point. Water would be one of the only common liquids whose thermal conductivity increases as the temperature rises. Ammonia too, but there must be a few others.
Diamond conducts heat well if we don't burn it.
Aluminum alloys to lower the melting point? It also oxidizes on contact surfaces.
Silicones have a strong evolution potential; there are so many possibilities for variations that we are just beginning to discover them.
Mayonnaise, after all, already contains oil and water; we are heading towards a thermal paste...