Sorry to pick on you chef, but DJ is not OEM firmware, at least not in the normal sense. This is not the same thing as with Pioneer's 110/Buffalo's firmware equivalent.
The normal OEM situation is where you have a drive like the Sony DRU-810A which is actually an OEM BenQ DW-1640. The Sony OEM version has its own model numbering system which shows up even when you check the model number with software such as Nero Infotool. It also has its own specific firmware releases customised by Sony for its drives.
WIthout going into too much detail, DJxx firmware for the 4167B is meant for Hitachi's version of the GSA-4167B. Hitachi, unlike its ODD partner LG, doesn't seem to sell drives directly to customers. Instead its drives get rebadged by Japanese companies such as Buffalo and IO-Data. In that sense, the drives are OEM but that is where the similarity between this and the normal OEM practice ends.
No attempt has been made to hide the true manufacturer/model number of the drive, unlike the usual rebadging practices. The drives themselves although sold in boxes printed with Buffalo's or IO-Data's model numbers, reveal themselves as GSA-4167B when checked with a drive information tool such as Nero Infotool. They also have "Hitachi GSA-4167B" printed on them instead of an equivalent Buffalo/IO-Data model number. So this isn't the usual rebadging exercise. See here :
The firmware used by IO-Data and Buffalo models appears to be identical, implying that the firmware came from Hitachi and was not customised for Buffalo or IO-Data. Seeing as the firmware appears to be from Hitachi, which is LG's partner, this is hardly your usual third party modified firmware affair.
In any case, DJ13 has been tested on LG's GSA-4167B and it works very nicely. For any more details about this or the exact differences in the firmware, please see the following FAQ, which ala42 alluded to above (particularly Q6 and Q22) :