Reply to my own post. I spoke with a human associated with UPS, after waiting only an hour on hold. He told me that the item was categorized with HS code 9903.85.68, which according to him describes the part as being made of aluminum and therefore subject to a tariff of 200% of its value. It's not aluminum, it's plastic, so I have begun the dispute process -- again, to yet another different email address.
Then I looked up the HS Code. Beware Russian aluminum...
Derivative aluminum articles that are products of Russia, or where any amount of primary aluminum used in the manufacture of the derivative articles is smelted in Russia, or where the derivative aluminum articles are cast in Russia, when such derivative articles are provided for in the headings or subheadings enumerated in note 19(a)(iii) to this subchapter, or notes 19(i), 19(j) or 19(k) to this subchapter, as applicable per the date of entry for consumption or withdrawal from warehouse for consumption, except any exclusions that may be determined and announced by the Department of Commerce