it is most probably the pump, they crack after some time and need to be changed. I replaced my twice in 16 years. Buy a replacement pump (circa £23+P&P on ebay Dec 2008) and if you have some tools and a notch better than basic mechanical skills you can change it yourself. It is relatively easy. However... not as easy as the heater replacement (from the back) because you have too open the front of the machine. Unplug it and pull it out - it is haevy! Start by pulling the knobs off and removing the top pannel under them. Dismantle the front. The pump is in front on the left at the bottom of the machine.
The biggest problem I had was with the door rubber seal retaining wire. It is a bit tricky to bring it back together to close the machine. I used an electrical wire and an electrical pliers with v. thin round ends to pull the big wire circle together.
NB Use a tea spoon to remove soapy gunk from the pipes before you fit the new pump.
Voitek (Warszawa, Poland), December 2008