are common on OLD motors due to the hardening of the seals
. Placing absorbent pads under the motor
will keep the bilge
clean. The problem is, if it's the rear main seal, the oil is leaking onto the flex plate (flywheel) and slinging it all over inside the bell housing. On a car w/standard trany that would be trouble by getting the clutch
oily. But on a boat it MAY BE creating an oil mist in the motor
compartment and making a big mess depending on the design of the bell housing.
And are you sure it's the rear main seal. Sometimes the valve cover gasket leaks
allowing oil to run down the back of the motor. Unless the motor is clean it's hard to trace an oil leak.
Not knowing your mechanical skills or finances it's a hard call. But if it were mine I'd replace the seal. The smell of hot oil is not one of my favorites.