A little mould at the top of the cork, away from the wine should be harmless. Wipe the rim of the bottle - before opening - with a damp cloth and then check the bottom of the cork - the part which was next to the wine. If that is clear then it will be fine. If it is moulded then I would be very cautious about drinking the wine.
Smell the wine before you taste it. If it smells musty, avoid it.
Chat with our AI personalities
Yes, it should be replaced. If you cannot use it, use another stopper for wine bottles that are readily available from most good wine shops.