And here's an afterthought - to my knowledge the fabric did not come off the Spirit of St. Louis more than once, and that was the repair carried out at Le Bourget immediately after the NYP flight. Therefore the third photo in the last post (see below for a repeat) must be French, and from that occasion.
[Click thumbnail for gallery photo]
I must confess I had no idea that the French mechanics had to repair that large areas of the Spirit! But judging from the evidence here, it must be so.
Since the silverdoped part we are discussing is there in the photo, it must have been there for the NYP flight. And since it didn't come off, it wasn't part of the fabric covering.
Furthermore, I suspect there may have been similar silverdoped cardboard (or ply or whatever) reinforcement in front of the door on the right side. That is very difficult to spot, but it would be logical, due to the mass of fuel tubing, instrument wires, and lever wires on both sides. For modelling purposes, the inside of the door, plus the small area in front of it therefore ought to be silverdoped, plus the area we are discussing on the left side.