I found the water level sensor twisted a bit and when I tried to move it back, it came off and coolant sprayed every where.
It seems the lock in clips on the sensor had perished after 18 or so years and had caused the sensor to almost twist out.
As a temp fix I put a new heavy duty lock ties over it and it was fine
I would suggest if you have one of these you twist the sensor out anticlockwise and check its condition and if suspect get a new one (only cost AUD$17 delivered on Aliexpress) or run the risk of a coolant loss when you least expect it.
- new sensor
- old sensor perished lockin clips
- lock ties holding down old sensor