To answer a few questions.......
Since I am a long time gun owner and competition shooter and have experience in returning guns to manufacturers and gunsmiths, I returned the gun for him as he is fairly new to the firearms world. I was just trying to do him a favor. In retrospect, had I known that the gun would not be returned before he moved to MD, I would have had him send it back. However, once he moved to MD, that would have been an ugly can of worms in itself.
The other points brought up by "rusirius" are valid. However, when I asked the folks at Glock about returning the gun to the owner who now lived in MD, I was told that even if the gun is sent to them from the legal owner, if that person lives in MD, they will not send the repaired firearm directly to the owner. They would only send it to a FFL dealer.
When the gun was returned to me, there was a document in the box that stated that the serial number on the frame was a replacement for the original. Both serial numbers were indicated as to the original and the replacement. Additionally, it was stated that the broken frame was destroyed. (Incidentally, the broken frame was part of a recall by Glock. they had a bad batch of frames where the rear guide rails were breaking off which is what happened in this case)
Also, as far as Glock was concerned, since I sent the gun to them, they considered me to be the owner. Totally legal in the sense that I could have made a private purchase of the gun from my friend. Upon receiving the repaired gun back, I give it back to him. Again, a legal private transfer in Delaware.
Whether or not what the MDSP told us is correct, I don't know. But but by going through a FFL holder so that neither of us winds up in jail was the best course in my judgement.