How can I fix my vauxhall signum window wiper?

I have a 53 reg Vauxhall Elite and there is an intermitent fault on the window wiper some times it will not switch of and some times the blades just stop in the middle of the window screen and sometimes the washers will not work I have been told it could be one of the following faulty wiper switch, faulty motor or faulty relay. I have had it to a main dealer but they could not find any problem. Please could any one advise.