Major Steering problem again - lots spent no joy

Hello everyone the dreaded vibration through the steering wheel is back accompanied with a pull to the left/ n/s. The vibration only appears at 53 m miles per hour and only every now and then. The pull seems fairly constant although does vanish for a day or two its as if the tracking goes out and then resets itself. Braking is always even. The pull is the same under drive - decceleration or coasting in neutral. If it was constant then so much the better but it just isnt. Also when i go over a series of potholes I can get rid of the vibration and the pull but it always come back .
So far I have changed all shocks, all bushes to polybushes, new discs and pads new bearings, new steering damper, new track rod ends , new drag link end,new wheels and tyres non of which has solved the problem have checked the swivel ball joints both under load and when car is jacked up and there is no movement.
Dont know what to do next so any suggestions more than welcomed
Ta

Sorry meant to say replaced the suspension bags
Ta for any help

There may be no movement in the swivels, but that doesn't mean that the bearings aren't shagged. Someone may have just removed shims to eliminate the play, but the bearing could be sticky.

Okay thats good enough for me I shall replace the swivels and report back
Thanks

could it be the steering box? i don't know how, or how to check but you have replaced just about everything else!!!

Just a thought could it be the front diff I have a slight whine on overrun and havent investigated yet I just assumed it was the transfer box but it could be front diff but not sure if a diff problem would manifest itself like that but suppose it could be two seperate probs = swivel ball joints for the vibration and tracking and the diff for the pull??? anybody any ideas

took out the swivel ball joints on off side and top one was worn not too bad but enough doing near side tomorrow afternoon