That happened to mine, also. I thought I had some split gears when I tried to run it after several years in the box.
I just pressed the motor back onto the tape and everything's fine so far.
Flex-Seal or Flex-Glue, the handyman in a can? Some of the HO folks use RTV.
I suppose one could make a bracket or maybe drill a couple of holes and use zip-ties. Also, I'm told that the servo tape the flying aircraft folks use is super strong.
Rusty