I have a lot of grey ash deposit on the number 8 cylinder sparkplug. Its on the side electrode but the center electrode doesnt have any deposits . Other than that i cant find any black oil on any sparkplug so accordingly to Haynes manual i need to change my valve guide seals. Is that true or?

I just bought a new set of them because i guess i have to change them all while im at it.

 

I could be wrong on this one but i think the egr valve is closest to the number 8 cylinder. If this is the case this would be normal.