I did mine in January. I will agree, it wasn't easy (at least for me). It only took me 6 hours, but it was a painful 6 hours. I didn't have the snapon flex tool, but I did manage to do the job without removing the tensioner - don't ask me how because I really don't remember anymore as that was so long ago. That bolt Larry's talking about wasn't the problem for me - it was the lower "hex" bolt. There was just no way to squeeze a ratchet with an allen socket in that recess, unless you ground down the end of the allen socket. I ended up using the allen socket with the box end of a combo wrench wrapped around it for leverage.

I got that rubber hose Larry talks about from the dealer here. I think it cost me $16. The auto parts store where I got the pump had the same hose for $2.50, but since this is what I would call a "specialty part" and I was leery of being in the middle of the job and finding out it didn't fit, I sprung for the dealer part. If I had to do it again, I'd go with the $2.50 hose. But then again, we're only talking about saving $13.50 here - you're already saving a few hundred by doing the pump yourself.

I took the radiator out - it only takes about 5 minutes, no joking. Why risk a wrench slipping and putting a nice hole in the core? Besides, removing it allowed me to analyze and make sure it was in good condition. I was also able to see that mine was an "updated" radiator with the metal insert at the hose connections. Plus, with the radiator out you have a ton of room to maneuver.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280