We started with the smallest part, the head. The screws are freed and the top plate can be taken off.
The spring controls the movement of the top prism which still stucks.
The steel pin on top has been removed and freed some extra markings. The serial number is stamped twice and the maker of the head is Askania Werke (bxx). All other parts of the periscope are made by Leitz (beh). This is not uncommon.
The prism sits in a frame that must be able to rotate. The WD-40 shown in the photo provided the solution. The thick glass plate has a small chip, but after remounting it, this will be invisible.
Next problem is at the lower side of the head section. This side is protected by a simple glass plate, but you need a special tool to loosen the ring. The inside was dirty, so it had to be removed and cleaned.
There is always friendly specialist that can make the proper tool.
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