That's pretty bad customer service. Perhaps you can get the calibration spec from them? It shouldn't be much more than a simple (and very small) resistance value for the wire leading to the transducer. You might be able to splice it without a problem (as long as you seal it well - a tiny bit of corrosion would be a major problem) and just verify that you still have the proper resistance - worst case is that the speed indication will be off slightly but even then it would be off in a linear fashion.