Hi
ideally we need some photos
you can add some photos by following this great guide
[guide|21499]
That blackened grease could be where the switch has worn out and is no longer performing like a switch (turning in and off)
also I would check both sides of the board and check in power in side if the board, also check the fuse in the plug, but for now with no photos that's all I can really do so when we get some photos we can look into things a bit better;-)
hopefully this helps
Thanks:-)