A few months ago the nearside front breaks started sticking. I removed the pads, slide pins etc and cleaned them all up and re-greased them. A day later and they were binding again, so I pulled them apart again and re greased etc. When driving its barely noticeable until you pull up and notice that the car wont roll and occasionally you can hear a knocking noise as they cool down. There is evidence of overheating on the break disc, and the pads have crumbled slightly on one of the edges. When pushing the piston back into the caliper, it feels nice and free. The pads themselves are a tight fit. Could it be a case of new pads, or is it likely to be the piston sticking? The slides seem ok and movement is ok. Is there a common fault on the yrv? I don't want to have to buy new calipers unless I really have to.

Many thanks in advance.