I have the hardest time keeping my leaves spotless. Any thing seems to make a mark on them. I spay them once every month while outside with fungicide. Keep a close eye on this to see if it turns mussy. If so, cut it off down to good leaf. Other wise if it just turns brown, I leave it alone to help the plant produce more. If it brothers you, cut it.

The name is a contradiction. 'sayuri/Metallica' S. Sayuri is an aubrytiana family while metallica is another family which produces ' Siam Silver' or 'Tenzan' which look extremely similar but they are not the same. Sayuri is much nicer to own and produces more then 3 leaves to a stock and are hardier to keep. I own Siam Silver and hopping to replace it with Sayuri.

I can only guess at your picture but looks like Siam Silver to me.

This tells me the seller thinks they are all the same plant.

If that leaf is mushy, chop it off