When shutting Zanussi FL1032 door it does not trip the switch inside unless?

I have a Zanussi FL1032 washing machine. The switch that activates when the door closes has become very unreliable. Sometimes you have to slam the door several times before it activates, yet on other occasions, it works first or second time. I have removed the door switch unit and given it a bit of a clean. Thta cured the problem for a short while, but now it is back to being very temperamental. I suspect the whole assembly will need to be replaced. Do you have one and how much is it?