I recorded all episodes of the BBC R4 Life & Fate series in September last year, but now find that one of them (Fortress Stalingrad) is corrupted and unusable. Can anyone provide me with a copy, or point to where I can get one pls?

Couldn't say, other than keep on checking the following page to see if it becomes available.
http://www.bbc.co.uk/radio4/features/life-and-fate/