Changed my plugs for the first time yesterday and found one plug different than the rest. It was the cylinder (1 or 4, can’t remember which) on my passenger side (LHD). The outer-metal portion of the plug had what appeared to be dried-up water deposits(calcium-like deposits) on it and the top of the plug was very black. The electrode also had a bit more carbon build-up as well.
Any ideas on this?