To do the ball joints, you can either rent the tool if you're willing to do it yourself (I've never done it so I can't comment on the difficulty), or have a shop (preferably one that knows MB) do it. The cost is mostly labor and with the parts it'd be about $300 each, that's what one shop told me once. I think it's also recommended to have wheel alignment done afterward.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL