[C320-list] Perkins Engine Leak - little help needed

[Warren Updike]

Now, is my turn. Doing some light maintenance and noticed some fluid, maybe pint, collected in engine sump. It's light color, but has oily feel on fingers; and, has some dirt mixed in like it came from overflow bottle. Maybe coolant? I check heat-ex and it is full. Cap is new so don't suspect that. Check coolant overflow bottle and it is empty (always at "cool" line when cold.) Took bottle home and filled w/water left overnight...no leak. Hose connection from heat-ex seems tight with small screw clamp. No obvious coolant leaking on the engine or around the heat-ex.
How could coolant leak to sump with no obvious source?

Warren and Pattie Updike
1994 C320 "Warr de Mar" #62
Middle River, MD (Chesapeake Bay)