I was able to remove and replace the ball joints in my 560SL with this tool from Harbor Freight:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=38335

It's not very hard at all. My boots had disintegrated and my steering was affected by the bad ball joints.

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Mike Heath
1988 560SL Black/Palomino
1988 300SEL Black Pearl/Burgandy
1984 500SEC Anthracite Grey/Palomino