1989 Excella tank sensors

[crispyboy]

I am starting to tackle the next job - tank sensors and monitoring system.

The monitoring panel in my trailer is above the stove - part of the vent hood. It reads battery power and lp tank levels fine but the fresh/grey/black tank levels do not work - the levels always show full.
I opened the covers on the bottom and found "foil sensors" for the fresh water and black tank. Could not find the fresh water tank sensor.

1. Can these "foil sensors" be replaced?
2. Are parts available or am I wasting my time?
3. Does anyone know where the grey tank sensor is located?
4. Should I chuck the old system and install a new "Seelevel" system.

Any comments are appreciated.
Steve