Hello Christian
Have you considered putting the information you already have, including the pieces I have sent to you, onto the RAF Commands Bulletin Board. It is
http://www.rafcommands.com/ for the site and
http://www.rafcommands.com/cgi-bin/dcforum/dcboard.cgi for the forum and see if anybody there can suggest anything further?
Have you also tried checking German records for the period - local police in the area etc., as well as the German Armed Forces as their records might give you more information ?
I am sure that records exist for this aircraft crashing in Germany - even a Luftwaffe claim for shooting it down probably exists.
Feel free to come back if you need further information on crews etc. Please keep me advised of your progress, I just love being involved in solving a mystery.
Allan