ok, have now worked out that it's the front diff backlash that needs adjusting as it's set too lose, the bearings don't need replacing, but, there is a special tool that is needed to do this which ive seen on the net for $112 USD.
annyone have this tool I could borrow one weekend, or know where I could get one in the UK cheap ?
tool part number is 499787000 and looks like this:-
https://subaru.spx.com/Detail.aspx?id=168
it slides over teh output spline and rotates the plate which it protrudes from screwing it in/out to adjust tightness