Help me with this oil leak please!

[Al B]

I've pulled the lower tinwear off, cleaned everything up and run the engine up, result.........

...the motor is leaking from behind the crank pully, quite a dribble even when the pully is done up real tight.

Next question is how do I sort this? Would a 'Sand-seal' help? How come it's happened in the first place?

Thanks in advance for any help you can offer.

Al B