Remove the fan belts and let it idle. Cover and uncover the blowby tube in short..10 second intervals. The leak..if it's oil will rear it's ugly head. If it's a coolant leak, wash the engine off the night before and maybe drive 'till up to temp and shut it off. In the morning, go look to see if you have a cold water leak. Fuel, most of the time will only happen under a load and spreads itself all over. It sounds funny, but, clean the engine, let it dry, spray aerosol foot powder on the engine where the fuel lines are. Drive it in short runs, stopping every few hundred feet and look for the wet or washed away sopt.