WARNING: This page is about a different car, the 2008 Mazda RX-8, 2007 Mazda RX-8, 2006 Mazda RX-8, 2005 Mazda RX-8, and 2004 Mazda RX-8. However, it is still accessible from the selected car via links, so may be relevant.
Measure the clearance between the outer rotor and the crescent.
If the clearance is not within the specification, replace the outer rotor.
Specification
0.02-0.15 mm {0.0008-0.0059}
Fig 1: Measuring Clearance Between Outer Rotor And Crescent