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 V8 Estate [Organizers Choice FF15][2nd Place MK1 Class FF16]
02 SE SVT Wannabe
02 SVT Future Project