Definitely needs to be serviced by a properly Omega-trained technician who has passed the course on this problem, is thoroughly experienced & "au fait' with the matter.
I'm a little surprised no one has mentioned that before.
This movement (2500C) had a stopping problem which is remedied at full service by fitting a new style intermediate escape wheel in the movement & specific epilame treatments (which Omega ran training courses on).
To very briefly paraphrase just a couple of Watchuseek forum 'super-guru' Al Archer's comments :
Black sticky material built up on the intermediate escape wheel from the Cal. 2500C, & is what causes "the stopping problem" as it has been known previously on this forum.
Omega requires that when this residue is present on the 2500C, that this gold coloured wheel is replaced with one that has a different finish, and is more grey coloured.
In addition, a specific epilame treatment and oiling procedure is used on all 20 teeth of this wheel, in addition to the epilame treatment and 10 other points oiled on the co-axial wheel.
Please see the thread here : - https://forums.watchuseek.com/f20/po...ml#post7881654
IMHO, it's most important to get yours serviced by someone specifically Omega-trained & experienced with this particular matter, who has access to the correct new-style replacement parts, epilame etc.
It seems a few other forum members sent their watches to their AD/or other watchmakers (who had evidently not been on the course nor studied & practiced this treatment), the problem was not correctly addressed, & the watches needed to be sent again for service & the work done by Omega.
In at least one horror-story case (anonymousmoose) the watch needed to be sent back multiple times over several years, & evidently was never dealt with by anyone trained or qualified with the particular fault or proceedure, nor access to the correct parts etc, & was never properly fixed).
I've had both the 2500C (Omega in-house serviced) & 2500D versions of the movement in 1st generation POs for several years & they have been THE most accurate watches I've ever owned in my life, at times running within a couple of seconds a week or longer when worn contuinuously 24/7. (No other perceptible differences between the C vs. D performance that I've noticed).