You will need to remove the VTC gears to be able to check them.
The "back plate" is the part that interfaces with the cam seal in the head. Clean the back plate and then hold it with a latex glove on your hand to get a good grip. Spin the entire gear with the other hand and see if you can prevent the "back plate" from spinning with it. If you can keep it from spinning, the internal o-ring seal is likely ruined and this is the most likely source of the oil leak.