Timex Quartz Chronograph, Miyota OS 10
It looks like the o-ring of this watch had
been stretched, but ...
actually it goes into the groove on the case back which has a larger diameter. So it is still useable. First I thought it was stretched beyond good use, but then I found it still fits well. Besides the annoying finger print on the right hand side of the movement, the inside of the watch was very clean.