...a bio about Klemperer called Otto Klemperer: His Life and Times...
That, by the way, is a very good Klemperer biography (by Peter Heyworth), although rather difficult to find these days, especially the volume 2 (post-1933).
For the percussionists in our midst: even if he never conducted it himself, Klemperer did get to play a part in a performance of
M3 under the Mahler's own wand (the offstage side-drum: see Martin Anderson, ed.,
Klemperer on Music: Shavings from a Musician's Workbench, with preface by Pierre Boulez; Toccata Press 1988, p. 135).
(That's another book of interest for Mahlerians.)
(In which Klemperer also declares that the work that converted him into a true Mahlerite was actually
M8: "To be frank, it was not until [hearing Mahler rehearse it in Munich in 1910] that I understood Mahler's music well enough to realise what a great composer he was" (op. cit., p. 139).
PT