As Martin mentioned, at that age it wouldn't be powder coat.
I have many metal cabinets, alcohol I a good cleaner. You can use Windex or
simple green type cleaners too.  Simple green type however will leave a
soapy film that will need to be cleaned off.  I suggest once cleaned to use
a clear acrylic finish on them to protect it from rust.  Test an area such
as on the bottom to make sure your brand of spray paint is not reactive with
the coating already on it.  Your could end up with wrinkles and pealing...
Les

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