It comes as an assembly. Seeing it has a grease zerk, did you try greasing it to see if it tightens it up? If it still rocks and moves I'd get a new one in there while you already have things apart.
Should be the correct one.. but I can't bring up Demon so make sure it is... https://www.napaonline.com/en/p/NCN...r+Arm&impressionRank=2&keywordInput=idler+arm
