what can I check to find a small oil leak form intake when parked 97 mercury optimax

[seansboat]

1997 Sugar Sand Tango Jet Boat 105 hours serviced last year leak occured after a few tanks of gas were used this year.

what can I check to find a small oil leak form intake when parked 97 mercury optimax Jet Boat, what are some possibilitys?

thanks in advance