That's the heater bypass hose. Dorman part 626-207
. Available at Amazon.
Don't wait for too long or expect the stop leak to work wonders. The corroded part is steel and if it's leaking, the wall thickness is paper thin in spots and could blow out without warning.
It's a PITA to replace - you'll have to remove the intake plenum and other parts. So while you're at it, consider replacing the spark plugs back there as you'll have more clearance.
Here's a post
I wrote covering the replacement. See tips #3 and #7.
Last edited by rickpark; 03-21-2012 at 03:09 PM.