It will be a bit subtle, but yes! Those with light magic will notice how it slowly destroys the oil. The oil will converge to cover any holes, but it will be reduced. However, even the strongest blast of light magic will only destroy a small, thin layer of it. This is centuries of oil caked on here, so it will take some effort or perhaps a stronger source of light magic to get through this quickly...

(And of course, this is not the only solution! But it certainly is a good start.)