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Having just changed my spark plugs I have noticed white powder on 2 of the plugs. After searching the web I have read that this could be the fuel additive I'm using (Castrol valvemaster plus).
Any one got any comments on what fuel additive I should be using with unleaded petrol? Not modified heads.

I have been told you don't need to use them unless you are doing a lot of hard driving or towing. People have been finding on tear down on older engines no accelerated valve seat wear, using unleaded petrol without additive under normal driving conditions.