Why does everyone worry so much about a TINY little spot here and there or a little yellowing, plants go through stages as they develop, anything could cause anything, unless it spreads like hell and you can see it standing 10 feet away dont worry so much, you might just hurt it even more while trying to fix it.
just let it go by itself, these plants are stronger then you think.
You dont worry about a little spot on a plant in your garden and still its alive after 10 years not caring...lol...honestly itl be fine.
(Not offensive in any way just speaking my mind)