Hello - I have posted this information on other forums, and possibly even here somewhere, but I'll do it again quickly...
The 2 level co-axial escapement has an inherent design problem, which stems from the dual role of the upper co-axial wheel teeth, and the intermediate escape wheel teeth. These teeth are designed to fill 2 purposes, and the shape required for the teeth to do this causes a build up of sticky residue on these teeth, which eventually causes what is widely known on forums as "the stopping problem."
This problem exists on all 2 level co-axial designs so the 2500 A, B, and C, and others like the early versions of the 3313, etc.
Omega attempted to remedy this problem several times with different solutions, and their first attempts were not successful. In the end the procedures for the application of epilame to the co-axial wheel and intermediate escape wheel were changed, and also a specific lubricant is applied to all 20 teeth of the intermediate escape wheel, and it is applied in a fairly substantial amount (at one time these teeth were left dry). In addition on the 2500C, there is a new intermediate escape wheel used with a different surface finish, but since Omega does not offer a similar new wheel for the other versions, the real need for this new wheel is somewhat suspect in my mind. But as they require, when I service a 2500C that has this residue (most of the co-axials I see do, even if they have not yet stopped because of it) I always replace the wheel - it's only $20 or so and worth doing if it helps prevent this problem from coming back.
To the best of my knowledge, this last fix that Omega has implemented has mitigated the problem, at least to a point where the build up of this residue is not causing the watches to come in for service prematurely. But the inherent design issue, the shape of those teeth, is still there.
If someone bought a watch late in the production of the 2500C, then this new procedure would have been implemented at the factory, so in those cases it's no surprise that watches have run for a few years without stopping. It does not mean that they won't have this problem eventually, but it may not cause the watch to stop before it needs service for other reasons.
To me the fact that all current Omega co-axials are the 3 level design, which completely eliminates this problem, tells me that Omega thinks the 3 level is a more robust design and has less potential to cause them warranty problems. The fact that the 2 level design has been eliminated completely from their offerings tells me they are not 100% confident that they have completely solved the issues.
Hope this helps.
Cheers, Al
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