If you MacBook is under AppleCare, call them! They will replace the charger free of charge if you return your old one, you can either send it in or bring it to a store. If you are bringing it to a store, I recommend taking your Mac along to show Apple what happened on the MagSafe port, as they may replace it. However, I would definitely clean the port with a q-tip, and isopropyl alcohol (preferably over 90%, but 70% should work fine). Good luck!