Car wash's are notorious for that. I drive a 1965 Rambler and have had it for 22 years. I never take it to an auto car wash. If you have exposed mirrors, outside wipers and a stand alone antennae- your gonna lose something And it says in big letters NOT RESPONSIBLE FOR DAMAGE as you enter the wash.
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So you are screwed.
Plus car wash's are bad on the finish. That "wax" that they put on is the cheapest crap out there.
Notice the new cars. Hidden wipers, body hugging mirrors and no antennae. They will survive a car wash.
Hand wash it next time.