Triducer replacement for Tacktick mn30

I have a Tacktick mn30 system installed in 2011. The knotmeter has started showing zero all the time, even though the wheel is spinning freely.

Any options apart from getting a new transducer?

If replacing the transucer, should I get the DST800 smart transducer or the DST800 analogic? The current transducer is connected to the hull transmitter with separate wires for depth and speed.