Hi astrodog,
I am sorry to hear about your troubles with your used Sierra-1 purchase. To address some of your concerns, if the lead wires are actually soldered directly to the binding posts, there has obviously been significant tampering with the speaker and this would inherently void our warranty. In addition, if those lead wires are burned, this would indicate a significant current surge through the crossover and through one or both of the drivers. There could be significant damage to all of the internal components.
If the cabinets are in good condition and since you are interested in the NrT upgrade (which would replace the crossover and tweeter), my recommendation would be to keep the speakers and ask the seller for a partial refund, provided that he did not advertise them as defective. From there, send the speakers back to us for the NrT ugprade --- more than likely, you will have to pay for a new woofer as well -- but you might possibly end up with a set of Sierra-1 NrT's for a terrific price