replaced the top case (keyboard) on an '09 macbook a few weeks ago for the same issue. Now it works like a charm. found a brand new genuine Apple module on fleabay cheap.

charged $160 for the repair. which included new battery, just got a cheep-o one since it spends its entire time plugged in in a hallway(employee log-in computer). Basically just needed a cover for the hole and 30 sec of battery back up incase someone knocks that mag safe connector loose.