I removed the spark plugs today out of my 1989 150 Xp due to engine running rich. Portside had a milky looking residue on all three starboard where just fouled. Dark oily residue.
Is there water in the gas and why one side?
Should I get rid of the gas? Quite a few gallons left. Can I just add fuel additive OMC 2+4 or Seafoam?

A novice.

Ernie (E150TLCEM)