2nd, mine had this as well. I had to soak out a good inch of oil when I needed to change my plugs. Put 4 new seals (just in case) in the valve cover and problem solved.The cause of the corrosion and sludge shown in the photo from my post was a leaking spark plug tube seal in the valve cover on the #1 tube. Ever since the seal was replaced, the tube cleaned and a new spark plug and coil installed under warranty by Lotus I have not had any further trouble. Sometimes in absence of the black sludge where there is only the oxide formation the cause has been traced to water getting into the engine compartment, onto the valve cover and running into the spark plug tube.