I recently serviced this Omega Speedmaster Professional calibre 1861 for a ClockSavant customer. This is a beautiful watch. Sometime in the past, prior to the customer purchasing the watch, parts were swapped to produce this unique combination of dial/hands/bezel. The calibre 1861 is nearly identical in design to the calibre 861 with some cosmetic and a few parts changes. The 861 is itself heavily based on its predecessor, the Omega 321, also known as the Lemania 27 ch. The 861 varies in several ways including a “cam” to control the chronograph rather than a column wheel, a flat hairspring rather than Breguet overcoil, and other differences. Returning to this watch, though only from 2005, it was not immune to past servicing errors. It made its way to me because the customer dropped it. Falling onto its reset pusher, it broke what’s called a "stem bolt." The owner didn’t know it, but the accident only accelerated the inevitable as the watch train was struggling from improper oiling and another issue I discuss in a moment. The watch, as shown on the consolidated 4 picture image, had excessive oil. In addition, the chronograph driving wheel, which you will see at 9pm when looking at the back of the movement (first picture) was sitting far too high and only barely engaging the wheel of the chronograph coupling clutch. You want a good well-adjusted tooth mesh, not a marginal one. The driving wheel is friction fit and this wheel was much too tight. If you attempted to drive it lower for a better mesh, and many folks might go there, the watch will be damaged. It therefore needed to be broached to fit. It’s unclear to me, looking at the part, how this need to broach came to be, perhaps it was replaced in the past and not properly fit. The transmission of power to the chronograph is very sensitive and should be optimally adjusted to assure chronograph stability. The watch is now running beautifully once again.