Inside the control support on the left hand side there is linkage that connects the lever to the pto yoke and bearing assembly, inside the clutch housing, that provides the engagement of the clutch. There is a long nut connecting two threaded rods. On 4010 you remove the rod from the lever linkage and thread into the long nut to shorten the assembly to increase the pressure on the pto disk. Lever goes over-center to provide pressure. The 4010 pto bearing is greased from below after removing the cover plate. Foot clutch and pto bearings both have fittings. There is a detent plunger in the control support casting on the lever linkage that is usually frozen up that a shot of oil will help with. Keep stub shaft bolts tight. Normally rear main seal will not cause slippage unless clutch housing fills with oil. Hope this helps.        Edit: On a 4020 tractor turning the long nut DOES tighten the clutch as the rod ends have left and right hand threads. Your 4010 adjusts as described.