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I was bidding that but had to stop because pictures weren't good enough to justify the risk. Those MK1s are really special and rare watches so I hope you enjoy it in good health.
I have had watch hands get infected by mold, and the mold spreads only within one of the lume plot segments, gradually making it darker. It doesn't even cross over to the other lume segments in that same hand. Most likely, your lume is all original. However, if you don't like the way it looks, you can get it all re-done, but I don't recommend it.
Congrats on the sweet pickup. I may be in the minority here but I wear my 1680 and 1675 on five-digit oyster bracelets. I find them so much more comfortable and less rickety than the period correct four digit rivet or jubilee. Something to consider...