I've spotted some stains on the board and have reached out to David but unfortunately he is not sure what to do, so opening it up to the forum.
I've tried cleaning with detergent, vinegar and mineral oil. Once cleaned and slightly damp it seems that the stains have been removed but they soon appear once the board has dried. Applying mineral oil produces the best result but again the stains appear as the layer of oil wears away.
Any tips on reducing or removing this?