If you want to play on 3.41 you need to install the official Japanese 1.02 Patch [BLJM60273_[UPDATE_01_PS3FW_03.4100]_VER_01.02.pkg], in Multiman (or with FTP) go to /dev_hdd0/game/BLJM60273/USRDIR/SEC, and replace the files there from the original English release. (AG01, AG05, AG10, AG17, AG20 and AG22...)
On 3.55 it should work without the 1.02 Patch, but I haven't tested that, so if you have trouble Install the Patch, replace the files, and Enjoy!
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Finally after a very long search, i found the DLC for GranTurismo 5 - BCUS98114. Inside you will find the pkg with rap files needed for activation. Important guys, for this to work you will need reactpsn 2.26 to activate the DLC. I have tested the dlc and it works. The cars will be in the dealership offers. Don't make like me to look for it almost a hour , before i realize where to look )
The link is: http://uploaded.net/file/vkpg7it7
Extract the rar archive and there they are. Enjoy the ride. PSN games down loader and DLC, RAP files finder and downloader. Guys i can't remember when this was posted but i will post it again, a very big help for this tool in finding the DLC you want and get it, along with the files needed for activation .
Credits go to the original creator, here you go the link: http://ul.to/cuuk04vg
This tool give me the DLC i was looking for. Thanks to all who made this project go out for the public.