Thank you, Col, and thanks especially to you, Martin! It seems we had the exact same experience looking through the ORB; glad to know I didn't miss something there and that I'm not blind!
I found the names of the Do-18 crewmen on the luftwaffe-sur-zee website here:
http://www.luftwaffe-zur-see.de/Seel...n/Jahr1940.htm
They're listed as: Oblt. Heinrich de Vlieger (FF), Lt.z.See Wolfgang Cohrs (B), Uffz. Hans Liesner (HB), Fw. Helmut Suhr (Bm) - all MIA.
Hopefully someone will know something more!