I'm now most of the way through Series 2 of Old Survivors. There have been some cracking episodes, but it's not as good as Series 1. There are lengthy absences of main characters, and the plotting can be more patchy. The best episodes, so far, are the two London ones (featuring Trigger), and the worst is the Witch. Partly this is because the main character (Mina) is a poor actor, but also the dialogue is unpolished and the scenes are oddly cut and directed. This episode isn't representative, though.
Patrick Troughton turns up in one episode, as do Peter Duncan and Roy Cropper.
Still heaps better than the modern series.