I found a solution, or at least a workaround, for the problem with the failing OCS sensor. It would work on any car.
There's a part that is available through the website below that keeps your airbags on all the time. It's an easy fix - remove the part that is in the car and plug this one in instead. I just received mine yesterday, plugged it in, and was dismayed to see the light still on. I visited my wonderful mechanic, who plugged the car into a little device and turned off the flashing lights. Then he tested the sensor - yup! It's working!
The only teeny negative is that the passenger seat belt light is on all the time, as well as another warning light to tell me there's a problem. Those lights go off when I plug in my passenger seat belt.
The part is less than $100 with tax. Way better than the $3000 for a seat replacement.
https://airbag360.com/nissan-leaf--occu ... -578-p.asp
It's a good fix, with a few downsides:
1) The passenger airbag will always deploy in a crash, potentially causing injury to children in the front seat. Note: Children should not be located in the front seat anyway.
2) The passenger airbag will always deploy in a crash, potentially causing a dispute with your insurance company because it may cost more to repair in a non-total loss situation, or reduce the valuation of the car in a total loss situation.
3) IANAL, but I believe selling your car with this device installed is illegal under Federal and most State laws because it would be altering a vehicle safety system. I would personally recommend removing it before selling the car.
4) IANAL, but I believe it is NOT illegal under Federal law to install this device on your own car, however, certain states DO have criminal statues for this. You can get 1 year jail time and a $5000 fine in CA for installing such a device, for instance.  My state doesn't prevent owners from installing such a device on their own vehicle.
You can also buy a clip on ebay for ~$5 that you can plug into the passenger seatbelt slot so you don't have to use the actual seat belt to disable the warning. These are typically made for idiots (ie: people who don't want to wear seatbelts while driving). Yes, I just did call everyone who doesn't wear a seatbelt while driving an idiot. No, I'm not sorry. Wear your seatbelt.
 https://codes.findlaw.com/ca/vehicle-co ... 27317.html
Another inexpensive option would be to buy a seat from a wrecked Leaf on LKQ and install it. The seats attach with 4 bolts and are not hard to replace. You MUST make sure you get a seat with a non-deployed & functioning side airbag, and it must match your car's heated seat option. The seat would then have to be programmed by a Nissan dealer because the airbag will have to be paired to the car.