Probably one of the hoses on the underside of the intake plenum. When removing the plenum it is very helpful to romove the bolt that holds the metal fuel lines to the plenum (located near the EGR solenoid valve) that is just under the rubber intake ducting. Also a pair of long reach needle nose pliers will greatly assist in removal of the clamps on the hoses to the intake manifold. The plenum is a pain but it does come off. Replace ALL of the short sections of water hose on teh underside of the plenum. If you are still having difficulty email me for pics. email@example.com. Note that the coolant that leaked probably soaked into the exhaust manifold insulation so it will smoke like crazy when you start up again.