Super common problem with the switch. You can take them apart and clean them up but it's a pain. You can try and spray some contact cleaner in them to see if you can coax them into working for a while. The contacts get burnt and sooted up with carbon so they stop conducting. Cleaning them involves removing the contacts and removing the carbon. It's tricky and the parts are small and difficult to reassemble if you're not good at that kind of stuff. Another member recently fixed theirs somehow without taking them apart but I forgot what they did. Do a search for seat switch and you'll get a bunch of info. A search of youtube for g35 seat switch will get you videos of people taking them apart for repair. Good luck.

 

We fixed our passenger seat recently, you might be referring to us. The seat would move forward but not back, and the seat back would recline but not go back up. We took the seat out of the car, removed the switch from the seat and carefully took it apart. It's not as difficult as it's made out to be in a couple of older threads here but you do have to be slow and methodical when working on it. There are ball bearings and a metal strip inside the switch that get gummed up over time from a variety of causes so if you clean them and re-assemble the switch correctly it should work like new. Make sure the motor's getting power which it sounds like it is before you go to all the trouble working on the switch.

Edit: we did have some success a while back with the electrical contact cleaner but eventually it didn't help at all.