Diesel Fuel found in bilge pump compartment but Engine runs well and no visible drips in collection tray

[Cai]

I put dry pad under fuel filter, under the engine inlet and front of the engine, and they are dry, with or without running the engine. But after running the engine for about 30 minutes, I found diesel fuel in the compartment below or around the bilge compartment in my 1994 Catalina 320, which as shallow bilge compartment. no visible problem from the top of the fuel tank (28 yr old), no loose clamps as far as I tell. But the injection pump are looks shinning. Mysterious fuel has been hunting me for a week to find out, but run out of ideas.