Looks like a 2767 to me. Supposed to be gold cap , but that doesn't mean it wasn't stainless too. It is not a 2787, that is plain. If the back reads 2757 then something is wrong. We need to see more details of the sale.
Reference
KO 2767
International collection
1954
Movement
Type: Automatic chronometer certified
Caliber number: 351 / 354
Cal. 351
Created in 1949, 17 jewels, sometimes COSC.
Cal. 354
Created in 1952, 17 jewels, COSC
Both with central sweep-second hand
Case
Gold-cap on stainless steel
Case back
Press-in
Dial
With "Dauphine" hands
Click to expand...