I will start with your last remarks:
I don't dispute Gould's amateurish scholarship, but it doesn't matter to me, because he made the piano sing in the most beautiful way. I don't find the same compelling quality when I listen to for instance Angela Hewitt, only my opinion of course.
Since I do believe Gould to be a master musician and pianist, his interpretation of Bach rather reminds me of this Neuhaus quote:
"Rachmaninoff, playing Chopin as a genius but not a la Chopin, arouses admiration, in spite of his obvious departure from the composer's spirit, because his powerful personality together with unprecedented mastery will always carry away the listener and also because this is an elemental phenomenon which is not the result of a process of thought, of striving or of reasond preparation."
I feel it much the same way with Gould, who "shot first, and asked questions later."
We are in complete agreement here. (Except perhaps in regards to Angela Hewitt whose pianism I truly love). Gould was a master musician, and certainly a genius (and I abhor the theories that he was an autist which I regard as mediocre people trying to feel good about their mediocrity by labelling their superiors mnentally sick). As I said, I own most of his CDs, DVDs and I thoroughly enjoy listening to them. However, most of his interpretations (not only Bach's) are eccentirc to say the least. Again, there is no problem with eccentric interpretations except when people start claiming it is the real thing. I heard that Bobby Fisher invented some variant of Chess with slightly different rules (I cannot remember the details). Now Fisher's orthodox chess was exhilarating, surprising and powerful, and most chess entusiasts throughly enjoyed his games - in spite of all his idiossincracies and eccentric behaviour (which usually drove his opponents round the bend). However much one admires Fisher, one would not now claim that because he was such a chess genius that the game he invented is actually the true game of chess, after all who knows what the original game of chess was like anyway?
So with Gould. A master musician with refreshing ideas about music? No doubt. The best Bach interpreter? He does not come even close.
About the first point, Where were the faults or limits in Gould's mechanism? I've read it before on the forum that the main limitation was in virtuoso octaves; of course not an issue in the music of Bach. I heard another reference to injury in connection to Gould, and that was on the Taubman website. But honestly noting the prolific production of recordings, I can't see what injury anyone is referring to, and how it affected his piano playing.
Most pianists when they experience injury will hide it (after all their livelihood depends on being injury free). We might never know the exact details of Gould's injuries. However his playing - for anyone who is conscious of proper body use - is painful to watch (and I would say that it was also painful to do). Back problems at the very least, given his atrocious posture.
But here you make an assertion difficult to defend: that Gould was injury free was evidenced by his prolific recording. This is not true. Live concertizing is the proof of the pudding, not recording. It is perfectly possible to produce the most amazingly sounding recordings even if one is injured. thanks to all the technology at one's disposal - several takes, splicing, and so on. Gould was a pioneer and a proponent of using any technological wizardry to make up for personal limitations. The same way he doctored his piano to get him the sound he was after, he doctored his recordings (by the way, there is nothing wrong with that - everyone does it - which is one of the reasons you never hear wrong notes in recordings). Gould was not even averse to some cheating in the areas where he was technically limited (as you said, double octaves). When he recorded Liszt's trancription of Beethoven's 5th symphony for CBS, he played the virtuoso octaves in the right hand by using
both hands and overdubed the left hand afterwards. Obviously one cannot get away with this sort of thing on a live concert.
Moreover, you can record a piece bar by bar over many days, and an injury would not be nearly as crippling in such circumsntances as it would be in a live concert.
So, Gould's recordings produce no convincing evidence for him being either injury free or possessing a superlative, limitless technique.
About his retirement, Gould himself said that the explanations came later. He was "pleased" to discover a thesis that confirmed his innate discomfort and disgust at the performing scene.
Gould was a supremely articulate, intelligent man. If you ever get one of his DVDs, where he is interviewed by Bruno Montsaingeon, you might be totally surprised (I was) to learn that that very spontaneous, flowing interview was completely scripted and painstakingly rehearsed by Gould himself. Burno never got a chance to ask any question. Gould asked all the questions, and Gould answered all of them, Bruno being just his mouthpiece.
And about the second, I really can't think of any Gould recording where the counterpoint seems limited or suffering from mechanical want. Many times I've put on his Well-tempered Clavier recording, and pulled out the score, with the intention of following only this alto voice all the way through, or this bass, et cetera, and have been amazed every time at the purity and individuality of phrasing in all the voices. Same with the Art of the Fugue, and also with his Beethoven recordings. Am I perhaps listening for a different aesthetic? Though it seems to me the aesthetic of counterpoint is the pinpoint balance between the horizontal and vertical, which I find Gould achieved time and time again.
Compare it with Tureck's (WTC 1953 recording, reissued by DG, and 1986 Goldberg Variations recorded in St Peterburg's)
Best wishes,
Bernhard.