Weld On plastic adhesive.

I'm certainly not an expert on the subject, but I believe that before new "glue" will work the old adhesive must be cleaned out of the joint. I don't know where you live, but most major cities have someone who specializes in acrylic...they sell bulk sheets, tubes, etc.; they fabricate acrylic furniture, signs and parts. They know how to work with acrylic. I would check the yellow pages or do a Google search. You might find a pro nearby that can do it right.