From an RV Doc reader:
What to do? Well, ALWAYS turn OFF the circuit breaker on the campsite pedestal before you plug or unplug any shore power or extension cords (The RV Doc's been telling RVers that for years!). After you're securely connected, you can then turn on the pedestal breaker. The bad news is that if your plug contacts are already pitted from years of plugging or unplugging under power, there's really nothing you can do to restore the surface. Sure, you can use a little emery paper to brighten up the copper surface, but deep pitting means that you must replace the power cord. Make sure you get all the connections wired correctly though, as an improperly wired shore power or extension cord can create a dangerous hot-skin condition. So check with the manufacturer or get a certified RV technician to wire on a new shore cord. Nobody wants to be shocked (or worse) from their RV.