Thermo paste
 

Most heat transfer paste products are rated up to 300 degrees. I use Silicone Solutions #SS-240. It is rated for over 600 degrees. Non hardening. It comes in a 3 oz squeeze tube and is enough product to last a few life times. About $20/tube. I use it for both Lycoming and Rotax engines. The key is to use it SPARINGLY!

I was just talking to my buddy yesterday about spark plug anti-seize. I did a little research today on it because I need to buy (something) to keep on my shelf.

The Wacker P12 thermal paste is what is recommended (see Page 16 or 19 of the Rotax Illustrated Parts Manual for the 912 or 912iS engine). Here is the datasheet for it. The main characteristics for this silicone paste is the operating range (-40 to 200C) and thermal conductivity (0.81W/mK). It is made as a heat-sink paste for electronics, not an anti-seize paste for engines (though it does have some lubricating qualities). This posting seems to indicate that factory testing shows it "reduces spark plug temperature by 10C", though I was unable to find an authoritative source.

That said, Lockwood aero seems to have Rotax Part #897186A listed, which is a MG Chemical paste. I'm not sure where this A part # came from, as I don't see it listed in the latest Rotax manuals. Perhaps Lockwood realizes that Wacker P12 is hard to find and uses something else that they found to be adequate.

One that was mentioned earlier was MG Chemical 860.. which has slightly less thermal conductivity (0.66W/mK); SS-240 is 0.735W/mK; . Better than nothing, and probably more than adequate Search DigiKey for other options.

All that said, Hisco lists the Wacker P12 for it for $33 -- which is still theft, but not the grand larceny that CPS performs @ $164.