You would have to completely dismantle the whole console to get to the drive and then dismantle the drive, if you can get to the laser lenses you can clean them and see if that is enough and you can also try to fine tune the lenses they do have potentiometers on them, if you find the one for the blue ray you can do slight adjustments and with a bit of luck it will start reading the discs again.
Last step if those two don't work would be to change the whole laser assembly, e-bay is your friend here, I don't think you can find original parts for a price that would be justifiable.
Changing the whole drive is out because of copy protection, it will not accept a drive if the firmware doesn't recognize the mobo.
And yes as the person above says, get a new old one they are pretty cheap.