I had the same issue with mine (daughter driver) though the pads were also worn as were the rear discs so I replaced discs and pads at rear then went to front and stripped those down, I found nothing wrong other than the dust boot on one caliper piston had split and that piston was sticking/seizing.
I pumped the piston right out and cleaned it up then coated with Red rubber grease, its lasted two years like that but the same problem is back so I'll be fitting a new caliper next. as they're almost as cheap on ebay as a refurb kit.
I pumped the piston right out and cleaned it up then coated with Red rubber grease, its lasted two years like that but the same problem is back so I'll be fitting a new caliper next. as they're almost as cheap on ebay as a refurb kit.