Nice WP. Where did he serve? Cheers, Richard.
From the Lexikon der Wehrmacht:
Grenadier Regiment 726
Created on 15 October 1942 by the renaming of the 726 Infantry Regiment of 716th Infantry Division in France assumed. On 13 April 1944 became part of the Eastern Battalion 439 as V. battalion in the regiment. The regiment was employed in the summer of 1944 in Normandy, where it had suffered heavy losses. It was subsequently reorganized, but in the Colmar bridgehead in 1945 destroyed again.
Installed on 14 new April 1945 on the Upper Rhine from the staff of the old regiment, the First Battalion of the Rifle Training Battalion 75 and the Second Battalion of the 195th Infantry Training Battalion
Grenadier Replacement Battalion 216
The last service records in Gefreiter Günter Sielemann's I.D. are in the Fall of 1943. I suspect he did not fare well in France most likely Normandy in the summer of 1944.
The Wehrpass was issued to a Gustav Sielemann born in Bielefeld Schildische on 01.11.1908.
According to the German War Graves website he was died in april 1945 in the Kriegsgefangenen Lager Borisov