Champthekid
5904
Try a watch case opening ball.
I avoid opening watches for the most part , but these really work. 
Google them. They are on Amazon and a bunch of watch repair places online.
Case back opener
Hi friends, may be one of you can help me: I am looking for a case back opener for my Universal Genève Polerouter Sub ref 20369/1. The case back is 14 sides (7,5mm long each) and 32,3 in diameter. If someone knows where to find a such specific case opener...
Try a watch case opening ball.
I avoid opening watches for the most part , but these really work. Google them. They are on Amazon and a bunch of watch repair places online. ...
Recommended by my watch repairer for a vintage watch.
1. First, put some fine penetrating oil around the join between the case back and the case and leave for a while. Then attempt to open with a ball etc. Cigarette-lighter fuel has good penetration as an oil and worked for me once. 2. Place a cube of deep f...
Thank you Clive, but may be first I will go there
And if not to expensive, I would have the right tool made, I will keep you informed ...
You can buy three polygon opening pins for a standard opening tool.
Also there are Breitling 14-sided case opening dies in three sizes, one of which may do. Expensive but cheaper than special manufacture.