Thanks Wayne. My problem is that the only way o access the cabinet is through the drivers. There is no opening at the back of the cabinet, except for the recess containing the binding post. Yes, I thought of solvents but it will make contact with the finish or be absorved by the ply.
My other drastic solution would be to get another set of horns (H290?)and just drill holes on the installed one so I will have something to pull upon when removing the horn. Thanks again, Wayne.