A fluid spill from a broken street sweeper closed part of West Street in Danbury yesterday afternoon.  The hydraulic line broke shortly before 2pm near Oil Mill Road.  Traffic was diverted off West Street, with police closing both lanes of travel.  The oil slick travelled up Westville Avenue.  Firefighters put down sand to stop the flow of oil downhill.  A sand truck then dumped material in the area to soak up as much as 20 gallons of the leaked fluid.  The vehicle, owned by Danbury-based Hawley maintenance company, was later towed from the scene.