steering box or pump

hi got a 200tdi 110 and the steering wont return to centre when driving and is stiff to turn as well .it has power steering so i took the pump off thinking it was that put it in the vice and poured fluid in it and turned it by hand with my finger over where the pipe goes and it had loads of pressure and push fluid past my finger whilst pressing hard .so i gathered the pump is fine .so that makes me think is it the seering box thats the problem ? has anyone had the same problem.next thing is the steering box has 6 bolts on the top where it adjusts would a box with 4 bolts on top fit straight on or has it got to be a 6 bolt one just they look the same where they bolt on the chassie.

6 and 4 bolt are inter changeable ,4 bolt is a stronger box

james hi thanks just the 6 bolt ones seem harder to get than the 4 cheers

any 4 bolt will do ,disco defender are all the same its only drop arm that changes on late discos and they swap anyhow

Yes, they swap, but I've got one upside down in a vice at the moment and the bolt is a git to get off, and then I've got to get the arm off which is probably going to give me a hernia haha!