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Can someone post a link to a reputable source (preferably on Amazon) for aluminum blocks, nozzles, and tubes?

I tightened my nozzle and tube down as much as I can and I'm still getting leakage on the top of the aluminum block.

BTW, just want to make sure I have this correct - it basically goes nozzle, block, tube, and then there is a nut on the tube. That nut screws up against the carriage correct?