I had the same issue in My 2006 STR (jap) with the passenger front window.. just driving along one day and it decided to go down by its self and would not come back up, i then smelt plastic burning, so i pulled over and disconnected the the switch on the passengers door. Next day i checked it out and the passengers doors switch had completely burnt out. took it to nissan and they thought that not only was the switch buggered, but so was the motor in that passenger door. So i bought a switch off them ($75 from memory) and they wanted $611 for the motor, but i instead bought one from NissWreck for $150. Got home and connected it all up, and i still had the same problem, would try go down, but would not even attempt to go up... after many hours scratching my head and testing all sorts of things with a multimeter, i decided to check out the drivers door mast switches... pulled that all apart to find one circuit on the board to be burnt and broke the connection, i resoldered it and it worked again, both up and down. So i now have a Passenger front Window motor that i didnt even need. Glad i didnt buy one from nissan like they said!
So might be worth checking that out before you spend too much $$$ on new parts
So if anyones after a front passengers elec window motor, i have one that i wish to sell!