7.4 mpi Mercruiser oil leak?

I have a 98 Formula 252 SS with a 7.4 mpi Mercruiser, Bravo 3 outdrive.....I bought the boat 3 years ago and have been restoring it slowly...Ive been very good about properly winterizing the boat , even though the only water she has seen in this time has been on the trailer in my yard with garden hose attached....she runs perfectly. I changed the plugs, plug wires, oil, oil filter, fuel filter, flushed the fuel tank and she really just purrs, the bilge is clean and spotless..Well..the problem occurred forty minutes out on my maiden voyage...she ran Great , even though top speed seemed to be way less than i expected...I kept checking the engine like a nervous father and sure enough while sitting in a quiet Cove idling without making any noise.. i literally watched the bilge start to fill with all the fresh oil! I shut her off and haven't been able to find the leak anywhere? I cleaned her up back at home filled her with oil and she started emptying it out before I fired her up? Oil pan doesn't seem rusty...semms to be leaking from the rear of the engine somewhere that I can't see..Well obviously I'm gonna pull the engine but thought you might have an idea. T