If you're worried about disc reading issues on your Wii U, maintenance and salvation is at hand with the official Wii U Lens Cleaning Kit. If you did regularly use a cleaning kit on the Wii ...

(scratches only matter for the bottom side) Note: Loading discs with your finger in the hole is not healthy for the Wii U disc drive nor the disc. 2. Put the disc in with the label side facing up ...