Fabia oil leak - please help!

Hi,

I have a Fabia 1.4 MPi, 8v, 2000 X-reg.

I have an oil leak. It appears to be a slow one, leaving only 1 or 2 drops of oil on the drive each night. On inspection it appears that the source of the leak is behind the biggest wheel on the pulley (at the back, at the bottom) on the left hand side of the engine (drivers side). There is some oil sitting just under the wheel and on the tray underneath.

What is the most likely cause of this leak, would it be a leaking crank seal? My mechanic friend has taken a quick look and believes this probably the fault.

Any suggestions/advice much appreciated!