6 September 1975: broadcast of second episode of Terror of the Zygons. The Zygons brag to captive Harry about their control of the Loch Ness Monster / Skarasen, and unleash it on the Doctor... There's also a particularly chilling scene with the Zygon which is imitating Harry Sullivan.
6th September 1980: broadcast of second episode of The Leisure Hive. The Doctor is forced to age by the Argolins.
6 September 1986: broadcast of first episode of The Forbidden Planet (Trial of a Time Lord #1), starting the belated Season 23. The Doctor is captured and put on trial; flashback to the somewhat incomprehensible beginning of the adventure on Ravalox.
6 September 1989: broadcast of first episode of Battlefield, starting the last season of Old Who. Yay Brigadier! Lots of nice scene-setting, and then a knight materialises and addresses the Doctor as 'Merlin'.
6 September 2002: webcast of final episode of Real Time. Evelyn is saved from cyber-conversion, but the ending is kinda confusing.
6 September 2014: broadcast of Twelfth Doctor story Robot of Sherwood. Who was Robin? And what is a legend anyway?