braking sound when stoping at low speed only

[goldenbird]

When braking at high speed nothing is heard. when trying to move slowly down a hill by exerting a light steady push on the brake pedal, a sound is heard. The sound look like as the pads & rotors are wet with water. The sound is of low pitch. The brake oil level is at the middle, according to user manual you need to add brake oil. Technician told me to do not as it is a normal indication that the pads are about to worn out soon. brake light didn't light up yet to indicate the pads need servicing. Should I add some brake oil ? can I totally reply on the brake light to presume pads are good?