Replacing the valve cover gaskets revealed the #2 exhaust rocker arm looks darker than the others. Looks like carbon buildup. What does this mean? Bad valve guide/seal?
This engine has 180k miles on it.





The right bank looks okay. Maybe a little between 3 and 5.

 

personally, i wouldn't care too much.
is it the cylinder at the rear of the engine? potentially heat "damage", which could be an oil passage blocked on the cam-shaft caps or the rocker arm itself.

carbon build up looks like, well, carbon, and if the valve wasnt seating and you were getting blow by, you'd expect it in the pattern/shape of the valve, and not the top of the rockers...