Also check the heater hose where it connects to the top of the intake manifold, and the upper radiator hose connection to the thermosat housing. If water seeps out around these hoses under pressure it runs onto the hot intake and just evaporates right away. You can usually stop the seepage it by just tightening up the hose clamps a little.
IIRC on some trucks there is also a mismatch of the hose sizes for the heater hose connections. I think one hose is 5/8" and one is 3/4". Many folks try to use the same hose size on both fittings and don't get a good seal. The heater hose fitting screwed into the intake is also available in either 3/4" or 5/8", and someone may have used the wrong size. If they decided to use one of the fancy chromed fittings for the heater hose or thermostat housing it is also harder to get a seal.
I would also consider replacing the overflow tank. I could never find a leak in mine, but replacing it seemed to keep the fluid level much more constant, so I think it did have seepage somewhere.
Bruce
