I started using merc clean #2 in my 200 efi 3.0 litre. I have recently noticed a good amount of sticky carbon residue around the outside of the propeler. Is this normal? I have always used marine stabil in every tank and regular merc clean but they started making the different levels of mercury treatments. I started using this about a month ago and since then I started seeing the residue. Maybe this is a sign that it is working?