I would definitely buy a new lettuce clip for $1.00 and probably a new powerhead for <$20.00 rather then take a chance. You can always keep them for the QT/hospital tank. I just saw pictures of you tank (looking excellent) and I don't think saving $20.00 will be worth killing all your inverts.
That said, I dont think the amount of copper that has soaked into it would actually affect anything. Copper is a trace element found in the ocean and in most salt mixes (including Instant Ocean), just not in quantities that would harm inverts. The thing is, how can you know what ppm
of copper is in your powerhead and lettuce clip?