more on c280 wp leakage
Larry Bible is right on the button with the pain and suffering on the fan bolt. I have a 300TE so I have a little more room, but here's a trick I've used before. Cut a 5 mm allen key on the long (handle) side. Take about an inch or inch and a half off. Put the stub in the bolt head, then either use a 5 mm combo wrench or a small socket on it to remove the bolt. I've used this strategy on several really tight allen head bolts with great success. The transfer case fill plug on my 4matic is a 14 mm allen head plug and the $20 allen head socket will hit the friggin' exhaust pipe with a ratchet on it. I put the socket in the bolt and bust it loose with a 14 mm combo. Works like a champ.
The rod for holding the fan clutch still while loosening/tightening is supposed to be 3/16", not 1/4" (per the manual, honest!) I know that's close, but I have a 3/16" piece and it works like nobody's business and I've heard of others besides those in this thread complaining about how their "self-made" tool did't work well. The chrome plated heavy duty hangers you usually have at work tend to be exactly 3/16" OD, don't ask me how I know.
As for special tools, most pros have the Snap-on flex drive allen wrench for the water pump bolts in the back, but it can be done with straight extensions and a combo wrench(royal PITA). Three of the wp bolts are hex head and on mine, the bottom forward bolt was an allen head. Don't ask me why, that's what I had and I guarantee it was original. I have the manuals and CDs so I printed the specific pages out of the cd's for all of the work so I wouldn't have to flip flop through and smear even more grease on the pages of the manual than there already is.
Another BTW, the tensioner is mounted with a y-shaped bracket. The bottom of the y is to the passenger side. The passenger side bolt hole is open to the engine through the timing cover and a common leakage point. This is a great opportunity to clean the hell out of the area and reseal this point with non-MB approved orange hi-temp silicon Permatex. Apply sealant to both sides of the bracket (engine side and bolt side). My front doesn't leak anymore!
And last (I promise), this is also an obvious good time to replace the drive belt. The tensioner is much easier to set than the manual shows, too.