Anti-freeze leak...please help diagnose

I recently bought a 2002 Dodge Intrepid.  Runs great, with no problems until it was suggested that I get the anti-freeze flushed.  This was done by a local oil change facility that neglected to bleed off the air out of the system afterward.  It started leaking under no pressure and gets worse with pressure on the system.  I was told it was the water pump, so I changed that.  I was told it was the thermostat housing gasket, so I changed that.  I thought it might be the coolant resevour, so I pulled that and checked it, but it is fine.  It starts leaking, do to gravity, right after I fill up the resevour.  It is a constant drip.  Under pressure it flows heavier.  

Can anyone tell me where I can look next to get this resolved?  Thanks