I recently had my TPMS sensor replaced on my '09 Maxima. A few weeks later i ended up getting a nail punctured in the tire and drove flat for awhile and ended up having to replace the tire. I can now see a crack on the valve stem and I have to fill my tires every 2days. I have two questions:

1. Is it possible to replace just the valve stem and not the whole sensor?

2. My lease is up in January, so I'm trying to spend as little as possible on this car. Can I swing it with a non-OEM sensor without having too much issues with the TPMS light?.