There are several recordings of Brahms 2nd PC with Richter. Two of them are in my view the best: one with Erich Leinsdorf and the Chicago Symphony Orchestra, the other with Lorin Maazel and L' Orchestre de Paris. Richter did not particularly like his Leinsdord recording but he is not to be taken too seriously as he did not like most of his recordings apparently!
I personally think that both recordings are excellent indeed, but I am particularly fond of the second one (Maazel), for rather subjective reasons: I was at school when someone in my class gave me a cassete with this recording and I fall in love with it! Richter's sound is so identifiable there, so unmistakably his! Maazel has done a splendid job with the orchesta - which is particularly crucial in this concerto, a work that I think could be considered as a "symphony" with the participation of the piano.
Richter has played this concerto pretty early in his carrier and has performed it dozens of time. (I was thinking the other day, in what ways the approach to a work can evolve, if performed so many times! I normally manage to play a work (in public) two, maximum three, times. How my performance would be after, say, 50 times? I just cannot imagine!).