I'm very pleased with my minty 1940's Marvin - in no way to be confused with the modern company which purchased the name and claim to offer an historic identification service (they didn't reply).
I picked this up in Budapest.
I kept passing a rotary display of watches in an antique shop window. I had no idea what it was but it stood out among more expensive brands. Eventually I went in and found they were asking a little over £100. They said their watchmaker had said it was all original and intact, but he could not get it to work. So I took the risk and later came across a couple of Rolex/Omega certified watchmakers in Zagreb, Croatia.
Both assessed it and said it was all original, intact, 1940's, and had never been worn but stored in a drawer. The old oil had seized the movement over time.
The watch maker I chose dissembled it and put it in a chemical bath, reassembled the movement and oiled it.
It runs fine - gaining a minute or two a day. I was charged something like £80 for this service - I tremble to think what it would cost to have that done over here.