Thanks for the photos and letters....very interesting stuff.
Looking at the artifact ,and possible attachment points,the piece outlined in the attachment below, looks somewhat like a mounting tab to me, along with an indicator by the pattern left behind,... that the fastener was held fast to whatever it was attached too, and the head passed through the tab.( If that is what it is)
Research on the Lorraine -Dietrich engines haven't yielded any clues thus far ,as to the identity of the artifact , and it's belonging to that particular engine. ( will continue the effort).