Thanks for the comments Olaf. Yes this D minor prelude is flawed, as are many of my preludes. They just always seem to elude me at the crucial moment no matter how well I prepare. I'll keep working on this one (as well as that darned D major). The F major is not beyond reporach either. Luckily I have the fugues to compensate
No I have not got that top D in the last chord of the fugue. In my Urtext that D is an octave lower which seems to me more logical, and sounds better too. I'd say that top D is probably a Czerny "improvement".