They aren't supposed to be glued together so I suspect that's someone's attempt to repair them. The outer plastic part should just clip in to the aluminium inner.
To glue them together if they won't hold themselves together I'd recommend a 2-part methacrylate adhesive designed for plastics with low surface activity - these often come with a primer / activator solution which is usually MEK, a fairly vicious solvent. From memory, the strips are polypropylene which is a pain to stick with normal adhesives.
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