The float in liquid cylinders is typically an aluminum rod of a specific length, weight and density. As the liquid level changes inside the tank, the float rod allows the spring loaded gauge to rise or fall proportionately. If you gauge shows full all the time, the float rod has disengaged and fallen off the gauge. Perform a level gauge replacement per the operating instructions. The relief valve on my LWD for the LD series is weeping.
Some evaporation takes place every day.
The expanding liquid nitrogen must escape somehow, and the relief valve provides a safe way to relieve this pressure. If the container has enough pressure to withdrawal liquid, then the weeping is normal. If the container has no pressure, and will not deliver liquid on demand, the primary relief valve should be replaced. Always replace the primary AND secondary relief valves. Always test relief valves after installation and before putting the unit back into service.