Well that answers a problem i am currently facing. I too bought a 'Truck sat nav' from ebay. after reading your reply I checked mine and i think my 520 too was hacked to make the truck nav run. My 520 is currently faulty, so I bought a 530 as a quick fix on the grounds that it had an an SD expansion slot and would accept my truck Sd card. Having come here and read a few posts I now know it wouldn't work.
I was thinking of officially updating the maps and device. but it will be a waste of money methinks? If i understand my problem properly.. I either need to buy a device that will accept my SD card. or.. hack my replacement Go 530! Using anything but Tomtom to do my artic truck navigation fills me with dread! I need a solution fast. However, spending £300 on a new model isn't one of them!