State/DTC is usually the authority, but since he's AD I don't know if it changes things. If you don't find a arfcommer that knows for sure, here are some links to Uncle:

www.bis.doc.gov/About/reslinks.htm

The GI you want to mail it to should get in writing permision from his Commanding Officer. Also he needs to research German Gun Laws and the SOFA (Status of forces Agreement). German Gun laws would only apply to the GI. If you wanted to donate it to the unit..........It'd be US Government Property and immune from german law. I'm no lawyer but a Master Sergeant did just that with his carry piece when I was stationed in Spain. He got a Guia (CCW permit) for government owned weapons as Americans couldn't get a Guia for privatley owned ones and "LOST" it and paid a dollar (his selling price) for it when he left.