Technical Power Steering

[AnfielRed118]

My power steering fluid level keeps dropping as though there is a leak but i can't spot one. There is no oil deposit on the ground when it's left stationary or visually within the engine compartment. Any ideas what might be happening? A local motor factor "bod" showed me some additive that apparently softens up the seals if there is a leak and supposedly stops any leaks. Anyone used this stuff before with any success (sorry i can't remember what it's called).
The actual steering performance is no different even when the level does drop.

Any ideas would be welcome!!!