SD, I'm thinking of getting a GPS-Sounder combo, would you say it's better to install a new transducer specific for the GPS? and get rid of the old one?
Since I'm not sure I will go with the GPS, just a stand alone depth sounder made sense to me initially, but by what you said I think it's better to use transducers specific to system/brand.
The transducers are probably made by Airmar, who makes them for many of the major manufacturers. Unless you know what brand instrument head was supposed to be used with them, identifying the transducer may do you little good.