a fix for coolant leaking from the head is not tightening the head... unless it is a water fitting that is leaking, the head needs to be removed in most cases.
if the top radiator hose is leaking, then you can replace that and if it is new, you should be able to tell.
if your not sure... you need a second opinion and fast, your mechanic said it was leaking but from where? what did he suggest that the dealer should do?
if it was me, I would start taking a log of what they said they did and go and see a trusted mechanic for their opinion.
if it is still leaking, it sounds like you have a cracked head, but they do not normally leak outside the engine block, but that will make it run like a bucket of crap and can cause fairly major issues.
if your not sure what is going on you need some help.