My dishwasher is playing up! The spray arms are not spinning, I have checked that they are clean. The heater is working, the water is coming into the machine and being pumped back out and the cylcle is taking the normal time, just not washing the pots! We have just dismantled the bottom of the machine and discovered a black oily substance on the parts under the spray arm. Can I assume that this is serious and arrange a burial?