prop nut

Frank another question for ya hope you can help, we just picked up a new boat 27 amberjack, it has a lowrance lcx 104c head unit with a thru hull ducer. Not sure the number on the deucer. Anyway we do not mark fish hardly at all and we have been catching fish. I've messed with the gain and filters but can't seem to get in any better. Can a transduecer wear out over time, if so What would you recommend would be a good match with this head unit. Thanks a bunch.