I did a stupid thing by trying to flash the firmware for the Chinese model on my router. Really stupid because I had read the wiki some time ago, and knew better (but forgot).

I'll try to be brief here because the general procedure is well established.  Here is a very good write up for the WDR3600:

http://www.theoutpost.org/6-techy/tp-li … ut-serial/

I just want to point out that this also works with this model.  I ran wireshark at boot and it looks for a file with a specific file name.  You need to name the firmware file "wr941nd_v6_tp_recovery.bin"