Hello,
Thank you for your response, Unfortunately I do not carry any parts that may fix this problem, Usually the slumping of the arm is due to the unit arm not being aligned and tightend correctly or the teeth that hold the arm steady, by the tightening mechanism, are worn. Please feel free to contact us directly at 714.385.0080 for further trouble shooting. You can also call JBJ lighting directly for spare parts ( if available) at 310.672.0480
Happy Holidays!
Walter F Marine Depot Customer Services