I started to fog my cylinders on my 1999 Mercury 135. When I started to remove the plug on top left hand cylinder, I realized it was some loose, not to the point you could lift it out by hand but it would not tighten up or be removed without a socket. I have noticed a large increase in fuel consumption and planned on doing a compression test later, but now with this loose plug issue I sure am some concerned. The plug seemed dark as if "rich" fouled. Any ideas on what o check and consider? Sure appreciate some ideas, thanks