The original would not have been stained. Why would they? - it's a camera not an ornamental piece.
In any case it would carry on changing colour with age, and according to how much exposed to light.
It's a utilitarian object - I'd suggest a utilitarian finish; raw linseed oil. Very easy to apply - has to be brushed out thin with no pools. Rubbed up to a polish after a week or so.
It was very widely used but gone out of fashion. Very easy to use - too easy for our modern fusspots! Produces a very nice semi gloss hard wearing finish. Subsequent light applications will polish up to a very attractive sheen - non of that thick gloss look you get with varnishes
Here it is on sapele (I think). Was fairly light at first now darker and similar to your original item. "Rich Mahogany" in fact. It's a moving target, it depends a lot on how much exposure to UV - which could lead to the impression that the outside has been stained, as it will be darker than covered surfaces.