Coolant leakage on 2001 Kia Sephia

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There is a round metal tube that appears to be attached to the back of the thermostat housing and is located above the starter, its been leaking for a while the tube looks pretty well rotted out, and I have been told by my mechanic that it is built into the head and cannot be replaced, I find that hard to believe, the leak has ruined a starter, the car runs great, body is in pretty good shape, I don't want to junk it because I can't get the leak stopped. Can you help me. Its leaking almost a gallon a day, that is the only place it is leaking. The metal tube also has a small hose that appears to go to the heater core. Can you help.
(2) Answers
If you cut the leaking part of this pipe off, is there enough left to put a longer hose on it to fix this problem?
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