I'm bored and have some excellent photos floating around so heres a guide for renewing the crank seal
If you have a leak coming from the left hand side of the engine (drivers side) and it appears to be coming from timing belt area the problem is most likely to be the crank shaft oil seal, to renew this seal do the following:
Firstly drain the oil using the sump plug at the rear of the engine and jack the car up on axle stands
Slacken the alternator belt and remove it, being careful not to damage it
Remove alternator pulley wheel by undoing the three bolts (the large one on the crank)
Remove lower timing belt cover (you have to take them all off actually)
Before you go any further ensure you lock both the flywheel and and the camshaft, to do this insert a small bolt (5mm I think) into the timing hole in the gearbox flange and a bolt into the timing hole in the camshaft pulley wheel (10mm I think)... or get a timing tool from citroen)
Right with the crank and cam locked you can remove the timing belt, to do this slacken the nut on the belt tensioner wheel and rotate it upwards. Now slid the belt off the pulleys noting which way round it is fitted
You should now be looking at this:
Hold crank pully in place (place two of the outer bolts in the holes and use a bar as a lever... do not rely on the timing tool to stop the crank rotating) and undo the bolt...
Remove pulley wheel
Remove the seal cover (might need to lever with a screw driver, be careful not to damage it)
Now remove the seal.... this is probably the hardest part!!... I would tap it with a screw and pull it out with plyers, but you may need to use a punch to weaken and distort it to make it easier (just be careful, only damage the seal!)
Now if it looks like the above photo good job! lol, clean all around the area, smear some fresh oil on the new seal and tap it evenly in place with a socket that bears directly on the outer edges of the seal (not in the middle! as that would distort it!)
Replace the seal cover, pulley wheel and tighten the bolt up
Now you can replace the timing belt, ensuring it is fitted the same way as you took it off. To tension the belt either use a citroen tool and the correct weight or the finger thumb method:
Find a largish allen key that fits into the square hole on the tensioner pulley and use this as a lever to rotate the wheel downwards so it applies pressure to the belt, tighten up the nut, now pinch the timing belt between your finger and thumb in the centre of its longest stretch (the front of the block), now gently tiwst the belt you should be able to twist it no more than 90', adjust if neccessary. Now remove the timing tools and rotate the engine 3 turns using a large spanner on the crankshaft nut.... now retest the belt and tighten if neccessary
Replace all the timing belt covers and the alternator pulley and belt
To tension the alt belt wind out the adjuster until there is approximately 5mm of travel in the belt if pressed firmly with the thumb, then tighten the alternator bolts up
Jobs a good un'.... drop the car to the floor, fill up with oil and go for a drive... don't push it too hard for the first hour or so (let the engine heat up so the seal can expand and do its job)
Hope this helps anyone
Mark