There's several possible sources for a leak to collect in that spot. Hose, water neck, thermostat gasket (more likely on the earlier models since they use a paper gasket instead of the split o-ring style), crack in the intake by the temp sensor from overtightening, or simply intake gasket leak - they erode near the very front ports as that's where the coolant goes through, so it could be leaking up at the front and migrating rearwards to pool on the intake.
Driver's side front eroded completely through at the top; this one was spotted leaking down the front of the head, though:
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Passenger side not much better:
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Richard