I HAVE RECENTLY PURCHASED A 1991 MODEL MERCURY BLACK MAX 150HP OUTBOARD WITH OIL INJECTION. THE MOTOR RUNS GREAT AND CRANKS GREAT, BUT I HAVE NOTICED A FILM OF OIL INSIDE THE ENGINE COWLING. (THAT PART BELOW THE POWERHEAD AND CARURATORS) I HAVE WIPED IT OFF, BUT WHENEVER I USE IT, IT COMES RIGHT...