Follow up: there was an eBay auction of a Wilton vise that said
quote
all WILTON products are accompanied by an uncoditonal (sic) warranty.
"RETURN TO ANY WILTON DEALER FOR A FREE EXHANGE (sic) FOR A BROKEN OR
DEFFECTIVE (sic) ITEM"
\quote

So I emailed Wilton to ask if it were true. The response:
quote
Wilton vises do have a limited lifetime warranty. Meaning, Wilton does
cover the main casting of the vise if for some reason it does break. No
wear and tear parts are covered by the limited lifetime warranty (jaws,
spindle, nut, base, etc), only the main casting of the vise. However,
the vise does need to be purchased from an authorized WMH Tool Group
distributor. Ebay is not an authorized distributor, ...
\quote

Bob