They use a different RCA gain on the "new" version of the V3 Mono amps. There is a common gain value between the two, which is "25 db", but the other gains between "old" and "new" are somewhere around "31 db" and "19 db", if I remember it correctly. As far as I know, nothing else has been changed between the two versions.
There will always be a small amount of defective units returned, because of defects during the 2 year warranty period, but none should end unaltered at the "sender" of a warranty unit...