Never had that problem, but I did have a chip on the bottom of my Garrett DD coil. I filled in the chipped area with JB Weld and it worked great. Still in place a year later. Not sure if it would work on the ears, but JB Weld is a very strong adhesive and works on most types of plastic.
I had the ears on the Minelab 11" coil after spraying citronella mosquito spray on the coil. I tried 2 part epoxy cement and it held for a little bit then broke again. In looking for what type of plastic it had the ABS/PVC symbols for the plastic content.