plug paste...

You want the right paste, for heat-conducting capability, not for anti-seize properties.  "Very expensive" is a relative thing, compared the the price of your engine...  Lockwood sells a small tube for $27, but you only use a tiny amount on each spark plug, so that's basically a lifetime supply.

Thanks.

what is the website address of Lockwood ? couldn't find it.

Is there any other options than the wacker p12?

https://lockwood.aero/rotax-912-s-914-lubricants-adhesives-sealing.html

Many thanks,

I followed the URL but no P12 there.

Is this the only option?

http://www.cps-parts.com/scripts/prodView.asp?idproduct=245