A machine that is not original all the way through is not really a collectable. Featherweights are not rare in the least, having been made for a very long time in mass quantities. So for me, I'd get a reproduction case and use it.
Our original case did stink pretty bad. We've gotten most but not all of that odor out, but like
Shelbie says when it stays closed for a long time it will still stink.
I'm not a collector but a user with a variety of machines.
Joe