Your
motor could be leaking a bit of
gear lube from the lower unit. If you had a
motor oil leak from the
power head it would be visible on the block and around the base inside the cowling. Also over time you would notice an
oil loss with the dip stick.
Gear lube looks just like motor oil when it breaks down, especially in
salt water. Check the tightness of the filler
plug and "o" ring on the lower unit...also check leaking when it is out of the
water on a bracket or mount.