The best way to trace an oil leak is by sprinkling the engine with talcum powder ,after washing ,of course.Any leaks will be self evident after running for a few minutes.
Both my last MD7A's spitted oil from the air intake. I never found a cure. However it helps to clean the air filter regularly (with parafin/turps or some such liquid). I liked the gimbaled egg cup idea from another response although how it would go in a sea-way would be interesting.
I placed a container with oil soak cloth underneath and just managed it, for several years. I bit the bullet last year for a number of reasons and put in a D1-20, at least for the time being oily bilges, smokey exhausts and oil trails on start-up are a thing of the past!