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Speaker Wire Connectors on Luxman Amp

I own a Luxman L-210 amplifier. It has twist lock terminals to connect the speaker wires to the amp.

I recently had to remove the amp for servicing and when I was reinstalling it, I had trouble connecting one of the speaker wires. The wire seemed to go into the terminal normally but it would not lock the wire in place when I twisted the terminal. I don't know if debris can get into the clamping mechanism preventing it from working properly.

Has anyone else had trouble with these connectors? Is there a way to clean the terminal of pieces of wire that might have broken and stayed in the connector?