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 RIP [Best Non-SVT FITF12][3/13 ROTM][7/14 ROTM][2014 ROTY][Best Engineered FF14]
01 SE The V8 Estate [Organizers Choice FF15]
02 SE The SVTedan
12 SE Hatch Sport & Winter Package, ST Front End