Richard, my studio partner is going to want to kiss you for that one!
It's driven him crazy for a long time - he had a previous partner who had a rev A 1176 and it sounded better than another one which had been refurbed by UA at one point and couldn't figure out what it is - he said there was something going on with that un-"fixed" one that sounded much cooler - a little more "noisey" but it was worth it for the great sound. That would definitely explain it!
Interestingly enough, both our rev B's are purported to sound sound slightly "noisier" (in hi-fi terms) compared to the rev D's and afterwards but there a certain "tone" to them the later ones just can't touch imo.