How can I fix my AEG 72620 Washing Machine?

The machine is working fine but for a small leak from the drain pump at the front of the machine. I have tried tightening the cover of the drain pump, but it did not solve the problem.(the impeller can be turned easily and the pump is not blocked) Should there be a washer to help with the seal in the the plug of the cover to the drain pump? There is no mention of a washer or replacement washer part in the instruction book.