Your watch is 100% legitimate, at least from the outside. I would suggest that you start by reading this article by our member
@mondodec :
http://download1644.mediafire.com/98y9cqnn97sg/zjzxx3wwtdh/omega constellation168.025.pdf
You have the correct case reference. It is a Ref. 168.015. There is generally an engraving on the back of the watch below the medallion.
View attachment 463619
Sometimes it can be polished off as it is quite shallow.
To answer your specific questions:
1. You need a special tool to compress the crystal and remove it. Then you have to know how to remove the crown. The movement will then be removed from the front. Do not take it to a "jewellery store", unless there is a AWCI (or similar certification) watchmaker on staff.
2. Crystals and crowns for this watch should still be available from one of several sources. Once you have established a relationship with a watchmaker, they will likely be able to order these for you. It could be that the crystal can be polished out and the scratches removed, or at least be made less noticeable. The crown is toast, and needs to be replaced. The crown for this watch is unique to this model.
3. Ofrei.com (which you referenced in your post) is a legitimate Omega parts supplier and probably has this crown in stock.
By all means, get the watch on a leather strap. Metal watchbands, with appropriate end-pieces were optional for these. However, these cheap "Spiedel" style bands tend to grind out the inside of the lugs over a long period of time.
For $10, you got a steal of an Omega. You can find these for sale on eBay occasionally, where in good condition, they bring quite a bit more than that.
Good luck with your restoration project.
gatorcpa
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