“Turned out for me it was just this insulating gasket in the outside of the port that was stopping it charging and I didn’t even need to open the back. When I found part of it still intact, I guessed partial insulation might be that causing a short. The gasket is made of very thin tape and sure enough when I made a copy and put that in, it charged fine on the new charger I had bought.”

INDEED!!! That was the same case for my macbook! the plastic film on the charger port was partly broken. I took off the rest of that broken film with a pin, then I cut out duct tape to fit and place around the pin connections, and that did the trick!!