I recently completed this job and wanted to pass on what I learned. Here's what I used to do the job...

(i) New HB, there's extensive info in other threads regarding the various versions, cost approx $90.
(ii) New bolt, cost approx $5.
(iii) Blue loctite.
(iv) Special tool to hold HB, cost with shipping approx $70.
(v) 17mm Allen key, at some point MB switched to a bolt head as opposed to an Allen socket on the bolt (ii), I had to cut 2" from the length of the key to make it work (I did that with a circular saw and a cut off disk and then cleaned it up with a small grinding wheel).
(vi) 36mm wrench (it's a common part for pedal bikes - see www.parktool.com), you need this to undo the nut on the fan.
(vii) You'll need something to hold the fan hub still while you undo the nut, there's a special MB tool but I had an adjustable face pin spanner (the pins fit in the heads of the small allen bolts on the hub), see http://buy1.snapon.com/catalog/pro_det.asp?P65=&tool=all&item_ID=5848&group_ID=603&store=snapon-store&dir=catalog
On my car undoing the fan was the most difficult step so be sure to have some good wrenches, there is very little space between the fan and the engine.
(viii) Torx socket to undo the tension on the serpentine belt.
(ix) Torque wrench (>220Nm).
(x) Some extension tubes to fit over the special tool (iv) (mine was about 20" long) and the Allen key (v) (mine was about 3 ft long).

The job is straightforward...

(i) Remove the under engine protector panel.
(ii) Remove the serpentine belt.
(iii) Remove the fan, this was the toughest part.
(iv) Remove the fan duct.
(v) Remove the old HB, as others I found it easiest to lock the special wrench with the extension against the ground.

Install in the reverse order. I torqued the HB to 220 Nm and then gave it an extra 90 degrees, I didn't have a big enough metric socket for the bolt but a 1 1/16" worked fine.

As I said above in my case the fan was the most awkward part (that may not be the case for the E320), so check you have a solution for that before starting the job.

Good luck,

Peter

Inted,

My car is a '99 with 75,000 miles and the HB is a known weak link (although more for the 320 than the 430), it's not that expensive to fix and can do a lot of damage if it fails.

Peter