I've now had two Airstreams do that - leak from city water connection inside - soon after getting them. I think the first few trips down the road tend to loosen a lot of things when the Airstreams are new. I've tightened them and haven't had problems with them after that. I also replace the plumbing fittings with brass shark bites whenever one goes bad. Those plastic fittings that Airstream uses seem to crack and break a lot - even just months into a new trailer.
I had the body of my city water inlet leak. There are two halves held together by four screws. I replaced the whole unit and later learned that sometimes this type of leak can be fixed by snugging down those screws. So if you are able to get a screwdriver in there, give it a try.
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