Thijs,
well, if you really want to pursue this further;
http://www.suchreferat-moskau.de/Unt...che_index.html
they can probably provide information on the Russian period. Please note that you do not need permission to get info from the former ZNS Aachen archives. Just write to the WAST and ask for copies of any records from the former ZNS Aachen records concerning Lt. Gottfried Dulias.
Only WASt records themselves are currently not open. I will check the records of DRK Suchdienst myself if Lt. Gottfried Dulias was ever recorded as "Heimkehrer".
cheers,
John.