The spring compressor was off Ebay... I looked and the same one is marketed under a few names. Kinetic, or Schley or JTC, but all the same.
I think I paid about $50.
The two black towers fit on two of the cam towers, and the long bar goes in to them to act as a leverage point. We used the holes either side of the center. The red handled lever arm goes under this bar and the spring hold down goes in the first of the 5 holes. It works great!
The best moment was when we realised that you cant pull down on the exhaust valve springs on #5 & 6 because of the firewall/battery tray area.
We reversed the spring holder into the hole right on the opposite end and pushed up to compress the spring. You have to be strong tho!

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2009 Mercedes ML320 Bluetec