Quote Originally Posted by GKR_17 View Post
It would be legal to apply a Nikasil coating on an engine that came with the coating as OE.
On second read, application or use of coatings are prohibited. It does not say except as stock.

So under a strict read of the rules, OE engines with Nikasil coatings are not legal. Clearly a stock engine should be legal, but it may be a very tough sell to say that this allows the coating to be reapplied if it is removed for some reason.