That was my thought, but it didn't hold. I'm thinking the threads that the screws go into are stripped, so I have a replacement motor on the way. The replacement appears to have red loctite on the screws, so hopefully that will take care of things.
The problem I'm having is with the screws that hold the motor itself to the frame. The screws come loose after about 5 minutes of flight time and then it goes into the Death Spiral.
Does anyone know the torque specs for engine and propeller screws? I have a motor which is constantly working loose and want to torque it to the correct specs.