Omega 2520: Running well but occasionally stops

Hello everyone,
I’m having an issue with an Omega 766.1201 cal. 2520 and would appreciate some ideas.[

I serviced the movement and it generally runs quite well and can run continuously for about 48 h. Initially I replaced the complete balance assembly with one from a 2520 donor because of a broken balance staff. On the timegrapher, the readings look good in almost all positions, with good amplitude and a clean trace. I thought I fixed the problem, the watch is freshly serviced and I can gift it to my wife, which I did.

However, while wearing the watch it randomly stops. Once it is given a shake or the crown pulled out and pushed in again, it will run normally again. Sometimes it runs fine on the wrist for a day, but then stops again out of nowhere. It happends at different times, the hands are not involved in the issue. I also demagnetized the watch properly so that should not be a problem. There is also no hair or dust. The mainspring is not sticky, moves freely and breathes nicely.

I will attach the timegrapher readings for all positions. Looking at them I could only suspect something being wrong in the CU (crown up) position. I realised that that the movement is very sentitive when it comes to oiling the cap jewels of the balance assembly. Maybe the oil in the dial side cap jewel is not uniform and thus creates this problem?

Any thoughts on what could cause such behaviour or and experience with this particular movement would be highly appreciated.
Regards

DU:

DD:

CR:

CD:

CL:

CU:

The watch will not fit my wrist. I have had the watch in my hand for around 1,5h changing positions, walking with it. But it never stopped. It is a bit random.
And strange thing is: Once it stopped and I shake it to run again, it runs very strongly again in all position and shows no weakness on the timegrapher. So it definitely does not stop because it has no wind in it.

I do not own a winder, but I was handling the watch, constantly changing positions and it kept running. I am pretty certain that the right screws were used but that is a very good hint. Why would that only stop the watch when it is being worn tho?

Yes everything was running free and as it should including the lash back.
The watch also runs absolutely acurate for days in several positions, only on the wrist it shows this strange phenomenon.

The 2520 has had all kinds of modifications made to it to improve the "reliability" of the movement, accuracy, power reserve, etc. If your movement doesn't have all the upgraded parts, it won't perform to the best that is can...

Upgrades go from the mainspring barrel all the way to the reversing wheels, with a lot of parts in between.

I was not asking for an exact diagnosis, just wanting to see if some of you have had similar situation where a freshly serviced watch runs very well in every position, only to then stop randomly while being on the wrist after a day of also running there perfectly. I am just happy for ideas or someone saying they had similar problems with that caliber.

Since I probably have to take the watch apart again, I will definitely check for that, thanks! At the moment the watch is running perfectly again since 1,5 days while being worn, but I just cannot trust it anymore. I am really really confused.

So there are different 2520s out there with different stages of those modifications? I thought they modified the ETA 2000-1 and thus created the 2520. If so, is there a way to find out by checking the serial number at what stage of modification my 2520 is?

Yes, essentially, depending on when they were serviced. If they were serviced at Omega or by a good Omega certified watchmaker, those parts would have been upgraded as part of the normal service.

Most of the changes that I saw were made before 2010, so if the watch was serviced at Omega after that, it is likely that those parts (or at least some) have already been changed.

One question - did you check for worn parts when you serviced it?

I checked if the pivots or teeth are worn, for endshake and of course the mainspring. It all looked rather in very good shape, not to say new. And since I got these good timegrapher results I did not further investigate.
But I do not know the service history.