Right this isn't funny, I had the M+S every single time, now we have good weather I can barely get it to do it!!!
I have now opened a used switch, cleaned it with contact cleaner and flushed it with WD40.
So now it is don't fix it unless it is broken (again) or drive on and forget it till it is pi$$ing down and nasty to lie under in the rain and try a repair!!!
I don't know!!!