how to sense hydralic oil level in glass tube in a hydralic pressure tank

Using Arduino Sensors
1

please suggest me how to sense hydralic oil level which is in a glass tube and is compleatly sealed and is actually the level of hydralic pressure tank.
please suggest me a sensor which can sense the oil level through glass tube from outside

2

Perhaps this : Gravity:Capacitive Non-contact Liquid Level Sensor(3mm TR,5V) - DFRobot
Read the comments, it does not detect water (also oil ?) when turned on.

3

Can you die the oil?