Hello,
Currently on ebay is a photo of AEG C.I C.138/15 at:
https://www.ebay.de/itm/orig-Foto-Ph...EAAOSwSE9gAuQi
This is captioned as FFA 42. This may be the case however, not the difference in the fuselage band compared to the FFA 42 machines shown in the Aviatik B.II thread. The markings resemble those seen on AEG C.I C.90/15 of FFA 9b.
A further AEG C.I photo is at:
https://www.ebay.de/itm/orig-Foto-Ph...0AAOSwnidgAuUi
Regards,
Clint