I highly doubt it's the head or the head gasket. You may be better off replacing the valve cover gasket. Even though he tightened the bolts, the gasket could be damaged and causing it to leak still. Just get the Fel-Pro gasket(rockauto.com is pretty cheap) and you should be good. If you have access to a 10mm socket and a ratchet with an extension, you can easily do it yourself.
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