Hi Nick Rose,
Just some guides for you to follow,
[guide|73193]
If you believe your drive cannot read or detect disc properly.
If im not wrong, as based on my previous PS3 defective lens repair, you need to source and replace the lens, but not the whole drive as I believe it is paired together with the PS4 motherboard, changing it will not work, i guess.
so in summary, you need to dismantle the disk drive module , open it up, check the part number / pictures of the lens, and find the parts at ifixit (if it sells), ebay, aliexpress, etc.