Edit: I changed to title to reflect more of a how too.
Here is what needs to be done to replace the rear cam o-ring.
Disconnect turbo intake and disharge plumbing from the air box, and throttle body, respectively. I removed the air box, and its bracket.
Remove chimney from turbo brackets,(seven 10mm bolts

)
Disconnect the oil feed line at both ends, then the lower coolant line from the turbo, you can leave the other end attached to the cam support plate. Be sure you have a drain pan ready to catch the coolant.
Seperate the down pipe from the turbo, no need to totally remove it, just let it sit there.
Undo the bolts that secure the turbo to the up-pipe. With the upper coolant line disconnected, remove the turbo.
Remove the up-pipe exhaust bolts under the motor. Then unbolt the bracket that holds the upper part of the up-pipe to the motor. This bracket has only two bolts securing it, however the bolt screwed into the side of the block is a pain to get out without a 14mm ratchet wrench.
Remove up-pipe and its bracket.
OK, now the rear of the cylinder head is accessible.
There are four bolts holding the cam shaft support on, where to the o-ring is located, two 12mm, and two 10mm. Pull them out and remove cam support.
The old o-ring will look like a beveled piece of hard plastic, well mine did anyways.
Pull the old o-ring off, and clean the support if nessesary, most likely greasy from the oil leak, the reason you are in here in the first place.
Lubricate the support and put the new o-ring on. Gently re-install the cam shaft support and torque the bolts down. 12mm bolts, 12 ft-lb, 10 mm bolts, 7 ft-lb.
The rest is just disassemly reversed, the eaiest way though, that I found to install the up-pipe bracket bolt to the side of the block, is to pull the short piece of hose off of the turbo oil drain.
With the piece of hose removed, it gives you a
littlebit more room to get the bolt started with your fingers.
By doing te job as stated above it was fairly easy and straight forward, and it was nice having the extra room to work with.
I hope this helps in taking this job on for yourself.
