After what seemed like an interminable time my Master Perpetual has finally returned from service by JLC. I had sent it in for a routine service and also a dial replacement. The old dial had some strange corrosion around some of the indicators and the moo...
It was with the wait, but I do wish I had timed when I sent it in better. It would have been nice to have for the Purists Perpetual dinner earlier this year.
The "corrosion" you saw might have been oil displacement. I've seen it on other brands' watches, usually ON the subdial, not on the outside edge of the subdial (dial). Glad it's back and healthy again! Enjoy! -Dean
I think you might be right about the displaced oil. Looking closely at the photos that seems like a very plausible explanation. It was in odd locations though. It wasn't just around the edges of the sundials but on the moon phase aperture as well.