Artboas -- thanks for the clarification on the transducers. My 37.5 had an ST60 depth unit originally, which was replaced several years ago with an ST60+. But the original non-retractable transducer stayed in place.
The lesson (which we all learn sooner or later) is that parts can be interchangeable, and thus we cannot be 100% sure about anything on our older boats, until we put hands on it.
As infuriating as troubleshooting can be at times, I still think that working on my old boat's problems is far more pleasurable than anything I can do sitting in my office.