how to tell if my clutch needs replacing?

my ford transit swb 2.5d v-plate (manual) is very hard to change gear the clutch pedal feels only slightly easier to push down and the engine has a slight over rev in some gears i have noticed a small leak of oil from behind the sump on the floor and also a whir/clicking noise from behind speedometer/instrument panel (possibley a cable to clutch housing im not sure if any connection to problem)what checks can i do before assuming it is the clutch that needs replacing

james josephs
August 2006