Had a similar engine pan mystery for years and just solved it yesterday. Every now and then would find a spoonful of liquid below the engine. Liquid did not appear to be coolant or oil or diesel, so assumed seawater. Re-bedded everything in the area and never discovered source, until yesterday. It was a small leak under the engine in the bilge pump hose which passes through the engine pan area. The leak was only active while the bilge pump was operating which was seldom. My mystery solved.