2001 transit steering

[ALZI1967]

Hi ,

My van is a 2001 mk6 transit 350 lwb - rear wheel drive with the 2.4 duratorq engine

Ive been having a few issues with the steering on my 2001 transit for the past 2 weeks

Some days the steering is nice and light , can turn the steering wheel with say 1 finger.
sometime later it will require a heavy pull on the wheel to turn it.

next day it may start off heavy then after 10mins will go light.

I thought i'd solved it with a fluid change as the old stuff was brown and yuk , but no particles of metal in it - just burnt looking.

so anyway changed fluid - it seemed to work fine the rest of the day . then next day intermittent light then heavy.- it doesnt matter what the engine revs are and its got a a new serentine(fan) belt on ,there are no fluid leaks anywhere on the steering rack or pipes..

After a couple of days of still intermittent heavey/light steering , I decided to stretch the pressure releif spring inside the pump apparently this should increase the delivery pressure. and for that day and the next . the steering went nice and light , just how it used to be.

Alas it didnt last..

its recently had its MOT , no play in bottom ball joints - only failed on o/s track rod end - replaced with genuine ford item.

im leaning towards the pump ,but Any Ideas ???? please help ...