The WD40 would be for the seat runners. In my case, and in most cases it seems, it was the switch that had become faulty rather than the motor. Replacing my switch fixed mine.
There's a motor on eBay (see below), but give Nissan a try for the part as well. Charles Hurst Nissan sourced me a new switch for less than the second hand ones that were on eBay.
https://www.ebay.com/itm/OEM-03-08-NISSAN-350Z-POWER-SEAT-TRACK-MOTOR-DRIVERS-LEFT-SIDE-Forward-Reverse-/372165207217