My 15" mid-2012 MB Pro has the same issues, but I have not replaced anything other than the charger itself. (Same issues with a brand new charger!) I'm thinking it's the mag-safe connector/circuit that has gone bad from too much stress on the connector while it was plugged in. I have worked mostly with it plugged in since I bought it new. I have owned several Mac laptops and have never seen this problem before on any of them...