You might see if the store will do an even exchange first. The likelihood of the next camera having the same problem I think is slight. It sounds like one of your channel amplifiers is off, and I would not expect to find that problem in an entire batch of main sensor logic boards (which have the sensor and channel amplifiers together). I haven't seen samples, but I assume it isn't subtle. And anyway, it will be easier for you to have the store deal with returning your first D700 to Nikon, than to have you deal with Nikon yourself.