Glad the new mainspring is coming in, and that you got the screw broken loose.
Broken mainspring can cause a lot of damage depending on the watch, so replacing the spring is something that all service centers and most watchmakers do as a matter of routine. I've received some watches in recently with broken mainsprings, and the first is a Panerai 112, where the spring broke near the inner coil:
Broken area of the spring:
Mainsprings often let go at their most stressed state, so when the watch is fully wound or close to it. When the spring is fully wound in this watch, the spring is coiled around the barrel arbor. When the spring breaks it rapidly uncoils, and the only thing that stops the expansion is the inner wall of the barrel arbor. When it expands to fill the barrel, it slams up against the barrel wall, and this imparts a torque to the barrel, causing it to rotate. The barrel teeth are engaged with the teeth on the center wheel, so the barrel can't turn, and in some cases this results in the barrel teeth taking damage:
The barrel is made of brass (rhodium plated) and the teeth on the center wheel the barrel teeth mesh with are steel, so the barrel takes the damage. In some cases though the forces can be carried further down the wheel train, so this is a Nomos I'm working on right now that also had a broken mainspring - again the barrel teeth suffered:
Again the barrel is brass and the center wheel pinion is steel, but the wheel portion of the center wheel is brass, and those teeth also took some damage:
New parts will arrive from Nomos on Monday...but the point is the mainspring is a consumable item, so it really should be replaced at every service. As Chris points out you generally never know how long the spring has been in the watch you are servicing, and you don't know what life it has left.
Cheers, Al
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