The consensus was that there was nothing inherently wrong with the design of the 2500c, even though most agree the 2500d is better and closer to the design of the 8500. The problem with the 2500c was the lubrication; it required minimal lubrication (as with all Omega co-axials), but in the early days of the Omega co-axial, Omega didn't fully understand that. So they applied the same amount of lubricant to the 2500c that you'd typically use in non-co-axial movement, which was causing many of the 2500c watches (most commonly first generation Planet Oceans) to freeze up or stop after a period of use. Many of those early 2500c watches were fixed under warranty by Omega, and Omega eventually figured out how to correctly lubricate the 2500c and shipped them with the proper amount of lubrication. I have a 2500c Planet Ocean with a serial number from shortly before they moved to the 2500d, and it has run perfectly for almost three years.
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