[Nick Beale]

ULTRA (or BONIFACE as they called it in 1940) comes to the rescue once again:

CX/JQ/314 16/9/40
10. Late on 15/9 Obltn. z. See Fräsdorff sent in a further report (cf. CX/JQ/307, Para. 8, CX/JQ/306, Para. 22, etc.) to KG 40 at Oldenburg: (1) Obltn. Gäbest [sic] in hospital with fever, possibly dysentery. Replacement asked for.

CX/JQ/319 18/9/40
24. On 17/9 Obltn. z. See Fräsdorff told KG 40, Oldenburg, that Obltn. Gäbert would probably be out of hospital 10 days.

CX/JQ/389 27.9.40
14. Source saw a document of 26/9 addresssed by Leutnant-zur-See Ullrich of KG 40 to Oberleutnant Berger of the advanced party of KGr. 126 at Nantes. This asked what had become of the daily report on the state of the preparations to the Commander of KGr. 126. Secondly, it ordered a Ju 52 to be sent on 27/9 to Wittmundhafen, with an intermediate stop in Oldenburg, in order to set down Oberleutnants Fräsdorf and Thees for a conference with the Kommodore of KG 40 in Oldenburg.
Later source was fortunate in hearing Oblt. Berger’s reply. He stated that the Ju 52 had left at 0800 hours for Wittmundhafen with Obltn. Gäbert who would furnish immediate report on the state of preparations being carried out by the advanced detachment. The preparations for the reception of KGr. 126 would be complete by the evening of 27/9.

CX/JQ/347 30/9/40
29. At 1200/29 an urgent request was sent to Oberltn. Gäbert of KGr. 126 (at Nantes) that he should at once find out and report to KG 40 to what extent anti-gas apparatus was available at his aerodrome, and how far anti-gas precautions had been delivered there.

I have a number of hits for Müller (unsurprisingly for such a common name) but none pointing definitely to KGr. 126. For example:

CX/JQ/258 28.8.40
12. Source saw a document, signed Müller, requesting immediate delivery of 100 x 1000 kg bombs for aerodrome (Platz) 531.
Source cannot remember previously hearing of Platz 531.