Thats a coolant passage used for a passage to the heater. It goes to the heater core. I don't remember if it goes to the valve just before the hose going to the heater core. I know that piece gets close to the fire wall, but what I have done was tap the block with a pipe tap and put in a street elbow. Then screw in a pipe to hose adapter. I don't think you can find a new one of those parts , But they don't look to hard to make.