I replaced the KES-430A Laser Lens Optical Pick-up in a couple used Sony BDP-CX7000ES 400-disc Blu-ray players I purchased recently.
Both units couldn't play DVD's and had trouble at times playing Blu-rays. No issues once replacing the optical pick-ups. Both units play anything I throw at them now. In any event, I documented the steps required to replace the optical pick-up, pictures included as well. For anyone interested feel free to check out my post over at AVSForum here