I have long loved Marcello's Il Andante Sostenuto from the oboe concerto, but...?

Although I can't help you with the oboe recording you are looking for, and although you seem to have disliked other transcriptions of the Adagio that you have encountered, I nevertheless would like to recommend a transcription of this piece done by J.S. Bach for keyboard (BWV 974) and performed on piano by Glenn Gould. It can be found on a Sony CD (SMK 52620). Although Gould plays the Adagio with ornaments (I don't know if they were Bach's or were Gould's additions), his performance is simply stunning, so tastefully and beautifully played, and imbued with a depth of feeling that s to the heart of this music, much more so than any other performance that I have ever heard.