Ford Ka power steering fault?

I have an X reg ka, the power steering bottle where the pipes go into have alot of seepage (which got advised on its MOT) well it has a slow power steering leak takes approx 3 to 4 week to run empty, i was told it can't be the steering rack because there's no black fluid out of the rack gaitor so it has to be on the low preasure side.

Also after starting the car and turn the steering wheel it goes heavy then light and it does the same when driving at odd times.

Has anyone come across anything like this before?