Image description: a screenshot from the Wikipedia page for the Doctor Who TV series, with a user-added caption that reads "Preserve the media you can before it's gone forever." The Wikipedia article reads, "No 1960s episodes exist on their original videotapes (all surviving prints being film transfers), though some were transferred to film for editing before transmission and exist in their broadcast form. [88] Some episodes have been returned to the BBC from the archives of other countries that bought prints for broadcast or by private individuals who acquired them by various means. Early colour videotape recordings made off-air by fans have also been retrieved, as well as excerpts filmed from the television screen onto 8 mm cine film and clips that were shown on other programmes. Audio versions of all lost episodes exist from home viewers who made tape recordings of the show. Short clips from every story with the exception of Marco Polo (1964), "Mission to the Unknown" (1965) and The Massacre (1966) also exist."
The problem with BitTorrent is that seeding libraries usually don't survive a change or upgrade of the client, you'd have to find all the original .torrents and point the client at the right folders, praying it doesn't overwrite the with empty files for some reason.