Note that the floating lens that is right in the middle of the lens mechanism shouldn’t be touched. It is very delicate. It may have dust on the lens but don’t touch this unless you really have to. If you do see some dust then use a CLEAN cotton-bud and carefully slide off any dust.
a) Use a cotton-bud and remove the built-up grease on the drive guide-rods. These are the 2 stainless steel rods about 5 cms in length, one on each side that supports the lens mechanism. They had a build-up of crud at the ends.
b) Use a cotton-bud and remove the built-up grease on the drive worm-gear. This is a single bronze gear that is about 5 cms in length and as it rotates then it moves the lens mechanism (which slide up and down the guide rods). You can rotate the worm gear and this will cause the lens mechanism to move back and forth. It will automatically reset itself so don’t worry about moving it, just get rid of any built-up crud that stops the lens mechanism from travelling from full inner to full outer position.
After doing that (and the previous fixes) then the PS3 started reading the disks again.