Hi,
I just bought a new motoro a few weeks ago. He slammed himself into the tank cover and got a cut on the outer edge of the bottom of his disk and one cut between his two eyes(forehead?). the cuts were not as severe as the one that your motoro seems to have but what worked for me was to do a big waterchange and add a double dose of prime, this will improve his slime coat. I did a 25% waterchange every 3-4 days and kept adding prime. I made sure that he kept eating and got a lot of nutrients. 2 weeks later the cut on the bottom of my rays disk is completely gone and the cut on his forehead looks much better and is starting to go away. Good luck!