If you have an oil leak coming from the left hand side of the engine (drivers side), and it appears to be coming from the lower timing belt area; the problem is most likely to be the crank shaft oil seal.
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 end of the crank).
Remove the timing belt covers.
With the crankshaft and camshaft locked you can remove the timing belt. Slacken the nut on the belt tensioner and rotate it upwards. Now slide the belt off the pulleys noting which way round it is fitted.
Clean all around the area, smear some fresh oil on the new seal and tap it evenly in place with a socket that bares directly on the outer edges of the seal (not in the middle! as this would distort the seal).
Replace the seal cover and pulley wheel then tighten the bolt.
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 twist the belt you should be able to twist it no more than 90 degrees, and adjust if necessary. Now remove the timing tools and rotate the engine 3 turns using a large spanner on the crankshaft nut…. now recheck the belt and tighten or slacken if necessary.
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.
Lower the car to the floor and fill it up with the correct grade of engine oil .