I recently had a call from a fellow whose Rolex Oyster-Date chronometer was acting up on him. I have maintained this watch for him for close to 20 years, over which time I had serviced it twice. Most recently in 2014. The movement is a calibre 3035. The symptoms he described indicated that the mainspring I had fitted when I serviced it last, had broken. He brought it to me to check out. He told me that for some time now, he had found it necessary to wind it manually in order for it to run. I didn’t open it while he was here, but I told him I would be checking the two reverser gears for faults, and also (perhaps) a worn rotor post. When I finally opened it, I found both reverser gears functioning as they should, and no sign of the rotor dragging.I emailed him and suggested that one of the obvious conclusions was that his wearing patterns had changed, perhaps due to a lengthy illness. He emailed me in reply and told me he was diagnosed with prostate cancer in September 2022, and he had been going through lengthy chemo and radiation treatments, and indeed found his activity levels greatly reduced. He had just received his last radiation treatment, and he thought his improved situation would see his level of activity return to normal. Long story short, I will service his watch and replace the mainspring.