wiper trouble

hello my front wipers are going dead slow across the screen and sometimes stopping altogether,any idea what might be causing it,been to main dealer they think the arm mech which will cost 240 quid to do, 50 minute job, but then they said might not be that might be the motor or something else,so bit stuck has what to do????
 
wiper spindles can sieze up - but can be taken apart and repaired quite easily :thumbup: