I can't seem to get this speck off of my crystal. The speck is in line with the 36 minute mark, above and to the left of the 9 on the hours subdial/totalizer of the chrono. I've tried microfiber cloths, running it under water, and pressing tape on it. When I move the slide rule, the speck moves with the crystal. Is it possible it's on the underside of the crystal? Maybe I'm missing something? I had it serviced last year (maintenance, not overhaul) but it hasn't been opened since.
It's more apparent in real life than in photos, so I circled it in the third photo below



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