I donít have anything to add to most of your comments. And I canít spend much more time on this. Just a few final points.
The agreement is primarily between Claromantanus and the correction in Sinaiticus? But the corrector is clearly a different hand who might have made his annotation hundreds of years after Sinaiticus was copied, and he might have used a different source to supply the missing verse. I wouldnít expect synergies within the correction to have any beneficial use in determining what Sinaiticusí own source document was, unless you start with the assumption that itís a forgery and the same person used the same ms to correct his own error in a deceptive way.
It seemed really odd that youíd say that the Sinaiticus copyist was so horribly inept in copying, yet he was letter-perfect in the very section where letter-perfect copying would detrimentally expose his forgery. Or could the greater attention to detail in the correction actually point to a different scribe at work there, which is what would be expected if it was genuine?
In that section the only variants I see are prophetian in Claromantanus and Sinaiticus, vs propheteian in Vaticanus. And alalazwn in C, vs alalazon in S and V (plus kai ligatures in S and abbreviated endings in V). Alalazwn is the more telling variant I think (a mistaken masculine ending as opposed to the simple alternate spelling of propheteia), so the nudge goes toward a Vaticanus match (or no match).
Second, you make a big point about the short line and indented kai. But Sinaiticus simply uses short lines and indenting on the next line as a paragraph marker. And he doesnít put all his new paragraphs in the same places as Claromantanus, though he does in this instance. He also uses short lines for stress, to make repeated words stand out for example, as he does with several lines in a row starting with panta or ou, which could also have been a factor in outhen eimi ending up by itself. To know whether the indented Kai is significant youíd have to do a survey of manuscripts to see how many use indented (outdented?) paragraphs and how many start a new paragraph at verse 3. If these are the only two, then yes itís highly significant. If almost every one does the same thing, not so much.
A lot of your conviction seems to be based on the cumulative argument, and since Iíve neither looked at the other htís nor studied Sinaiticus in any depth, itís not convincing me at this point.