Get the bits from All German Parts, they come with a guarantee.
Do not buy lower quality bearings, I did, and ended up fitting 8 to the Avant over 2 years!! (They weren't the cheapest ones either)
Why would you want to keep the original balljoint? If the bushes have gone, the joint won't wont be far behind. I have chopped out the joint from old ones, and the steel ball sits in a plastic socket!
I did a how-to guide on suspension bits - it's in Scotts sticky.