The last piece in the Leipziger manuscript with signature Becker II.2.51 is a prelude with a fugue. It has no named composer in the manuscript. However, based on the style of the piece I think it is save to presume Georg Wilhelm Saxer is the composer of this piece. The prelude is well written piece, with a strong motivic force, that is used through the entire piece. One could call it a Toccata, and with good reason. The fugue is like the other fugues by Saxer: very little musical development, just four expositions in a row, joined by very short episodic phrases. The overal effect is more like a concerto than a fugue. It is a great piece to play and (in my opinion) a great piece to listen to. Sadly, it's the last Saxer composition available in this manuscript. Even though I wish there were more, we have to make do with the five preludes, published on this site in the last two months.
The recording was done with the Hauptwerk software and the sampleset, made by Voxus, of the Matthijs van Deventer-orgel in the Grote Kerk, Nijkerk (https://www.voxusorgans.com/en/product/nijkerk).
Score available here: http://partitura.org/index.php/georg-wilhelm-saxer-praludium-und-fuge-d-dur-2