What is wrong with my Miele Novotronic W828?

Last few weeks l have had to open my door on my washer with the emergency door latch in the Fluff drain filter flap as when pushed the door button would not open.
Yesterday l put the washer on and after 5 mins in to the wash,suddenley the door opened on its own and the lights went out.Wondered what was going on and closed the door again,started the programme again and it did the same.
Now if l close the door with the ON/OFF switched off,then press it to switch the washer on the door opens and the machine wont start.
About 1 hour ago l closed the door and the lights came on and just thought to see what happened and the machine started to work on a final rinse then stopped again when the door opened after a few mins.Water came out and had to mop it up.
Then l put it on a spin and it kept workng until the end.
I rang somebody up yesterday and they said it looks like there could be something wrong with the Door Lock Mechanism,which is opening the door and stopping the washer from working and would cost up to £100 to replace it.Its confusing as why all of a sudden the machine wont open,then it will. Now if it is the door lock mechanism why is it doing this as if it has gone it woudn,t work at all when the door is closed and l start a programme.The washer yesterday woudn,t work when l closed the door when it was switched on as the door just opened and obviously when this happens its not supposed to!But why today it worked again with the door closed.One min can open the door normally,then l cant,then can start the washer then l cant.
I have had my washer for nearly 12yrs and it has been fantastic and has never broke down and was told this when l bought it as was expensive and would last.Do l pay a lot of money to get this fixed as when l do l know it should last me for more many years to come?
Can anybody tell me what could be wrong.Will have to get somebody out too look at it.Thanks