Hi Bruno_jo and welcome to the family!
First off, if you did really get the G73SW at that price you say (350), then let me say it is an unbelievable price you got!!!
I used to have the exact same problem with some keys myself, actually in that same area.
Mine were S,W and a few numbers. Of course, I've had it for a while now.
Eventually, i replaced the keyboard and that solved it permanently.
Although i cannot guarantee it 100%, it is most likely a HW problem.
I would recommend you, to take it to an ASUS authorized dealer/shop and have it replaced.
Unfortunately for you (because of the cheap price you got the laptop), your keyboard (like mine) which is back lit, costs around 80-100 euros.
Mine cost that much with the shipping (100).
Alternatively, you can always use an external usb keyboard (if you have it sitting on a desk usually)
BR,
Eros