My front wipers are driving me mad and i need help!!!

Few months ago driving down motor way pissing down with rain wipers going like the clappers then they started to slow down then they stopped across my screen which aint fun when bombing down motor way then you cant see all of a sudden!!!!!

So i manage to get home and think the motors gone so next day was gonna buy one but driving to work starts to rain think this will be fun with no wipers!! give them a go and they suddenly work fine?!?!
Worked fine for a while then suddenly they start to judder across the screen then the other day they stopped again and then yesterday they started to work fine again?!?!?

I'm baffled and i need help!!!!

I've been told its the motor then i've been told its the relay would like to know if its either of them or something else don't really wanna have to change motor and the relay its gotta be one of other? hasn't it??
