[Mg-mmm] custom duty on vintage car parts

[Dan and Jenny Fest (Coles Nurseries Inc)]

Happy New Year to all !!
I have a quick question... Every once in a while when receiving car parts from
the UK I get a tariff(customs) bill for the shipper.  It's always with UPS
never any other shipping service.  I was under the impression that antique and
vintage car parts were not subject duty.  I usually just pay it but as a
matter of principal, is this correct.  If not, can I get  a link to prove to
them that they are incorrect.
Thanks,
Dan