I just pulled the intake on my 99 5.4l this afternoon. There is a metal tube that looks like a press fit into the right rear of the manifold which connects to a rubber heater core tube. It has a pinhole just a hair above where it enters the manifold.
Is this something thats replaceable? It looks like a press fit into the manifold. I'd rather replace it than weld it. It looks fine from the outside, but I'd imagine the inside is seriously corroded, and welding the hole closed would be a short lasting band aid.

BTW, this is not the heater core tube that runs through the valley to the back of the water pump. That one still seems fine.