If you check out the information tab above it explains how the brand has changed hands many times over the past 65 years. Parts, and even paperwork, are never a high priority to the new owner I am afraid.

What drives me nuts is I would be glad enough to pay them even $500+ to get it fixed. I spent $85 in shipping to send it in. I mean at least give me a estimate. I was going to buy a new zodiac for Christmas now I'm not. Its the same joke with Ducati. I bought a 1198 in 2011. Paid a good penny. Tried to take it in for service and I was told the bike is over 10 years they wont touch it? I argued ..then they gave me a price to change timing belt $3k....What?? Im losing my mind. I did it myself $300 and yes 8 hours. I'm I gonna have to buy more watch tools and just do it all myself. This all supports my wifes' logic when she says "Why are you buying (fill in blank) it will only cause you aggravation taking care of it"  I 'm beginning to think shes right. Between cars, motorcycles and watches house appliances I spend all my time researching how to fix crap. You cant even find someone to do basic home repairs. ARGH!!!!!!

Good point thanks for your honest assessment
at least both parts are vintage and probably from the same Time period.

And yeah of course I will make sure not to wear it too often and only carefully around water while washing hands etc....

Since it's from a trusted seller I expect the movement to be original. the case at least is in strong shape (like new) and and the movement also runs strong for its unknown service history as well as all chrono function are working perfectly.

But now I have to await the answer and info of the watchmaker about the movement (which company is signed on it and if it's worth the work and worth to exchange the acrylic christal with a new one)....

With just the dial changed I don't know that I would consider it a Frankenwatch, that depends on if it still has the original Croton signed movement or not.  Its not uncommon that this happens, blame it on the companies using the same chrono movement ebauches and dials of similar size/style during the era.  Like you said, still a very nice looking enjoyable watch.  Just be mindful of moisture as it is not resistant in the slightest at this point.  That is likely what ruined the original dial.

Thanks for the quick response. So you support the theory of it being a franken watch like I am also suggesting... I brought it to a watchmaker in my town to open it to provide me with some information on the movement and the inside of the case may be it will shed light on it if more stuff is croton branded it is pretty likely that it has been put together with the dial at a later point in its history. The funny thign for me is that the patina on the numbers and hands seem to match so this consistency of aging made me buy it. Nevertheless this does not mean the case and dial where born together....

And yes I know i bought it already so to late if it isnt authentic. But I will still like it and wear it never the less. Its a vintage chrono with a lot of charme on the wrist so it will get wrist time if it was originally build like that or not. I am just curious and thought i would try my luck on here... and the first response is not promising

The best odds are that it is a Zodiac dial stuck on a Croton watch.  I have seen those Zodiac dials floating around Ebay for years and clamshell watches are super at risk of getting moisture in them that damages the dial over time, so they pick up whatever dial would fit the application to get it sold.

Somehow the other pictures of the back and sides cant be uploaded since they seem to be to big. At least one more works and this one shows the Croton signed Backcover.

I recently acquired a Zodiac Hermetic Branded Clamshell Chronograph (my best guess would be from aorund the 50s). And since I couldnt find a similar one anywhere online I am wondering if it is real or if the dial was put in this case from Croton. Since they are different companies. We all know companies used to cooperate with each other in the past so it could still be possible that zodiac bought the case from Croton and build its own Clamshell Chrono.

But the odds are low since i didnt find anything on Zodiac Hermetic Chronos from the 50s. It just seems odd to me that I cant find anything about any other Zodiac Clamshell Chronographs. I Can only find information about Croton Clamshell Chronos.

Any help is appreciated and very much welcome.

It's a vintage watch. Many brands will not service them - or do so at an extortionately high price. One reason is that parts are so hard to come by, that only specialists are willing to do the hard work and build up a stock of parts - or know where to source them. FG bought a brand name and nothing else. No factory, no machines, no tools, no parts - nothing. It was all lost in the turmoils of the quartz crisis and a 1999 bankruptcy. Hard to blame them really, what are they to do about it? At least they keep the brand name alive. If your local shop know what they are doing, you will be happier with the result and pay a fraction of the price that FG would have charged you, if they had taken it on.

Since they bought the brand they have never done anything with/for previous owners' models. They used to send them here.