So today I went out to fly a little. I put my mini 2 on the ground and hit the auto take off button it started up but one the top right motor was having trouble getting moving. All the others were fine and I did get an error message saying like motor cannot rotate or something like that. I picked it up and kinda hand spun the little motor and tried it again and it worked fine. I usually kinda spin the motors by hand before flights to check and that top right one has been a little stiff lately but just slightly more than the others. I think there is something slightly sticky on the pin in the middle of the motor and can see a little residue on it and I think that's what is causing it. Is there a way I can get in there and remove that grime? It's not bad and I don't think that it will lock up in flight with the motors fully going. I just think it had a little trouble getting moving today. Any ideas?