The left one is the idler with the jrsc kit. Good luck getting a hold of a new one. The right one is the stock idler which you can get a new one from any auto parts store.
I had the same problem. Replaced the tensioner and belt and it took care of it.
04 ZX3 Mostly Stock ["Best Non-SVT" FITF '12][3/13 ROTM][7/14 ROTM][2014 ROTY]
12 SE Hatch Sport & Winter Package, ST Front End
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