Thanks to both of you. The RAAF sources say the battle occured over "Bir el Zidan" and the German ones over "El Zidem". I have not been able to find these locations on any current map or geographical website, but the Pl.Qu given by Matti allowed me to find the general area. The complete Pl.Qu is 13 Ost/5287:
http://www.mapquest.com/?q=31.041666,15.583333
Best regards