Pliable, who has been drawing attention to some of my favorite records, most notably that Mahler 9th with Bruno Maderna on BBC Legends, has done it one more time. John Barbirolli's Mahler 9th on EMI is an excellent recording of that piece.
There is more to Barbirolli's Mahler output than that incandescent 9th. A few important and very interesting such records are a 1960 7th with the Hallé Orchestra and a couple of Mahler 2nds, one from 1965 in Berlin and another from Stuttgart in 1970.
That 7th is very interesting indeed, and probably worth your time. Barbirolli's interpretations tend more toward, say, the Jascha Horenstein side of things than the Pierre Boulez side. Still, it is interesting and engaging to hear what he was making bands that weren't super-familiar with Mahler do in the 1960s. This isn't flawless playing, well, the live records aren't, but it's worth a listen.
Then pull out Gary Bertini and hear Mahler that is both expressive and precise.