Remove the inspection plate and using a flashlight with the engine stopped carry out a visual inspection first.
Check and look for; Any pieces of clutch lining on the inspection plate or in the well behind the plate access. With the pedal 'up' there should be an even gap between the release bearing face and each finger screw. Have an assistant press the pedal. Check the amount of movement at each PTO adjuster screw as you prise the flywheel round. Are you able to engage gear smoothly if you push the pedal into the second stage? If so then it may be adjustment of the PTO screws is all that is needed. The standard gap is 090". This can be. It is not an exact figure but all adjustments must be the same. Increasing the gap will bring the second stage in later. Look for any evidence of oil contamination which would make the clutch lining 'sticky' and drag.
Let us know what you find.
DavidP, South Wales