You have to change the whole tie bar. I've just done mine, cost £26 for the tie bar from a local car parts shop. Jack up the car, support on axle stand and remove the wheel. Clean up the area around the inboard mounting and mark the position of the nut and washer with tippex. The nut and washer are eccentric and provide the adjustment for the rear toe-in/out so you want to get them back in the same position.
Loosen the nut on the inboard mounting then start undoing the nut on the ball joint. Before you remove the ball joint nut completely, jack up the suspension an inch or so to releive the tension on the tie bar. Once the ball joint nut is off remove the inboard mounting nut and bolt and remover the tie bar
Fit the new tie bar in the reverse sequence to removing the old one, ensuring the inboard nut and washer go back in the same position.
When you undo the outer ball joint nut the whole ball joint will probably start rotating as the nut reaches the rusty exposed threads on the bolt part of the ball joint. You can hold this from turning with a 5mm alen key in the end of the bolt but that means you have to use a spanner on the nut, not a socket. My allen key stripped it's hole because the whole thing was so rusty but luckily by that time i had exposed enough thread to get locking pliers on the shank to prevent it turning.
Tim, April 2008
