I'm thinking Winchester here? 10CSC is from an AS 1320 ebauche.
Yep Winchester from me too. Was their possible variant info for the shaded dial? I don't remember.
Here's a snippet from 1955 first party ad we got from Bruce Shawkey.
You siad subject dial shading is similar to your Watertite?
Winchester case for sure, but the hands are different from all the Winchester adverts.
The base line model looks to have had a plain dial.
The advert above details that the Winchester "B" had a black dial and the 1954 price guide only lists variants A and B at $75.
Could possible be a movement swap.
Tentative Winchester, for the same reasons as this other watch entry; The shaded dial available for the Winchester, as seen in the available ads and one posted model, does not match subject dial.
Ken, you make a good point regarding the shading. My thought is that the ad might be misleading, I can't remember a Bulova shaded as pictured in the ad. I'm going all in on the Winchester ID. I get it that a part or two may have been swapped out over the last 60+ years but I really think the subject watch is a Winchester.
In reply to Ken, you make a good point by Geoff Baker
Geoff, the ad does show an unusual shading pattern - certainly not the typical X that we often see; and there is one Winchester in the database already showing what appears to be the correct shaded dial for this model. A match to the ad in a Winchester case makes me feel the X type shading on this one is not correct for this model.
In reply to Geoff, the ad does show an by Andersok