According to the FP.-Nr. 20045 A (letter), Hans Mauckner was in the 14th company, Grenadier Regiment 423 when he was MIA.
The post war tracing service of the German Red Cross does not list him for that unit as MIA anymore.
Very strange, because on this memorial he is still listed as MIA.
Hope this link works for the DRK search site.
@ Peter U: Thanks for all the documents and your work!