What are you trying to get fixed? You might find someone in USa that can do the work
I know nothing of all the forms & paperwork needed to enter Germany & then re-enter the States.
However the above advice seems sound to me, just to keep all of the gun inside of one border in this crazy world.
Differing regulations & interpretations is a can of worms that I personally would not like to open & then risk losing parts of my gun to petty officialdom.
This also smells of costing lotsa money.
The current crop of Merkel workers may know no more about this gun than some one at home.
A bit like taking a 32 Ford into the Wayne Michigan Ford plant for an engine rebuild.
Just my opinion, whatever that is worth.
O.M