I was just watching 'The Time Meddler'
First encounter with another TARDIS.
I've never seen it before. I was waiting for them to slip up and for the 'Monk' to call his time machine a 'TARDIS' but he doesn't, just a Mark 4. (Susan came up with the nickname acronym TARDIS, it's not the actual name of the ship). Also no mention of Timelords etc, just that the monk came from the same place the Doctor did.
Anyway, the reason I am writing this is that an assistant came up with a very good point. . . and one that explains away a lot of 'why can't we just fix everything by going back in time again' problems. The TARDIS is broken, it can't be relied on to come back to the same place, let alone the same time if it takes off. The assistants are concerned that the Doctor decided to move the TARDIS to keep it out of danger (from flooding) but if he does, he can probably never come back.
Great plot/story device. If they land somewhere and some wrong has to be righted, then they have to do it there and then, no pissing about in time and space. I'd never thought of that before.
Next question. . .when did they fix that? He seems to be able to go wherever the hell he likes now. It still seemed to be buggered in Davisons time when he kept trying to get Tegan back. (and Baker dropped Sara Jane off in Scotland instead of Croydon).
PS
Peter Purvis is quite the rival for Bonnie Langford in the bad acting and badly written motivations awards.