The crank in 2005/2006 was modified to accept TWO keys, the bolt and cone were changed as well, according to the bulletin I have which is scant on actual details.
Remember the crank pulley key slot is marginal to prevent potential stress cracking of the crankshaft at the #1 web. (due to 5 cylinder crank stress.)
By virtue of its form, the strip key is only about 1/8" or 3 mm thick and about 4 to 5 mill wide so its hardly any good for taking a torsional load subjected by the crank pulley driving the accessory equation hanging in the front of the engine . Obviously if the pulley comes loose its inevitably torn off the crank and mashed up in the key slot!
Theoretically you could simply put the pulley back on without the key and tighten it down correctly and it would work.!
BUT
You need to have the pulley located correctly on the crank for timing purposes, and probably more important is the balance and phasing of the crank pulley/harmonic balancer arr.
(MB calls it a shock absorber by the way) .
So enough of debate & theory the question arises how to fix it without tearing it down some more (tedious task)
Traditionally I have simply purchased a key from MB parts and glued it into the open slot using Vic's favorite --JB WELD!---
using a some duct tape to hold it there until dry.
Now the other method I have used is again simple.
Obtain a new strip key arr' and cut it to fit into the vacant key slot and be long enough to stretch all the way back to the timing sprocket . Using JB gobwhack and duct tape recreate the original strip key when it was first installed & let it dry.
Now caution!
Its very easy to dislodge your "field fix" and end up like Mr Bean doing a jumping cussing fit!
Besides it can fall into the sump, and then its a fishing exercise.
So!
Take a file to the inside edge of the key slot in the harmonic balancer and file out about an 1/8 " metal on all three sides creating an 1/8 x1/8 (3mm x 3mm ramp).
Then you can carefully offer the pulley /balancer arr, without undue risk of dislodging the key or repair section .
Once offered up use the new crank bolt and washer to force/press the arrangement home and snug it up.
Then its Big Mamu time , lock the crank and tighten the bolt to
240 lbs ft ft PLUS 80 degrees angle stretch tightening. (heaven knows what is that final torque) .
As a footnote I have tended to follow the cut strip key technique for a field fix which so far after about 2 years of service duration been a 100 % success.
All the best
Dennis
p.s
For those with a tram lined crank stub having suffered some wear use Loctite Assembly Liquid.
Just remember this is almost a "final fix" so it will be a devil's task to remove the crank pulley again.
D