Thank You for using JustAnswer - My name is Tony and I am more than happy to help with your question today.Before stripping down the dispenser unit, try cleaning the distributor top with a toothbrush first.Siemens do have a web site where you can access drawings but that may not be neccessary.Let me know when you are ready to proceed.
I have already cleaned with a toothbrush as this it what other websites had suggested.
Can I assume you have checked that the water actuaklly flows through the dispenser top.It may not be the black mould that is the issue.
Yes, I've taken the tray out whilst machine running and water is coming out of some of the jets.
Out from some of the jets the lay above the conditioner tray?
If you take the top of the washer off you should be able to see the distributor is accessible.It will have 2 connecting hoses to the rear.If you disconect those hoses you could try flushing out the distributor with a garden hose or failing that remove the complete assembly to thoroughly clean it.
... think I'm going to have to try this so might be a day or two before i get back to you ...
That's OK just come back when you are ready.If you CLICK HERE you should be able to find the drawings. They may help a little