I went to PCW this morning, and they were selling the LG GSA-4163A for £59.95 including Nero, cables etc. I then bought the LG GSA-4163BA - as reviewed in PCA for £35.99. I presume it was OEM as the plain brown box contained only the drive and an additional silver bezel. Just installed it now and it works a treat.
PCW had craftily kept all the OEM DVD R/RW's on a rack at the very back of the store, I did not know they were there until Security Guard told me!
Must say that it works extremely quickly, only problem I have is that appears to take more electrical current compared to the CDV Rom Drive that it replaced. Ocasionally on initial bootup, the PSU cuts-out. Have to turn off the power supply from the mains so that the PSU resets, then reboot. May have to install a higher rated PSU. I will make a post on this to the Help Forum for sdvice.