Carbon build up intake port?

[E3AV]

There is some sort of grey stuff on one of the intake valves. Is this carbon build up? Why would it be in only one of them? Most of the stuff was on the valve itself.

 

[sfdon]

If it’s gray- pull the spark plug and if it’s gray and covered with thick goo- it’s oil and shouldn’t be there.

 

[E3AV]

The spark plugs are equally black in color and dry. Some of the plugs do have oil on the threads but here I’m suspecting a leaking valve cover gasket.

 

[sfdon]

I would suggest a leaky valve seal.