A site with an inventory page, which lists items for sale. Each item description includes a link to a spec sheet which can be downloaded in .pdf form. However, those items are eventually removed from the page, and the corresponding spec sheets become not available. This triggers a crawl error in Google webmaster tools, because it knows about the links, but gets a 404 error when it tries to visit them.
Should I instead return a 410 Gone error code? Should those links (to the downloadable .pdf file) be nofollowed from the very beginning, since Google can't index the documents?