Sorry my initial spouting off / thinking was too old school... Yes you have a wet clutch that's inside the transmission.
The control valve for it is external and there is one adjustment on it, If you can get to the valve In Picture 4 look at #'s 210, 200, 190, 180, 170 and see if they are loose. if they are it's probably come out of adjustment.
Also when was the last time you did a fluid and filter change?, being a wet clutch assembly it's susceptible to pressure variation due to restricted fluid movement.
#1 Wet PTO clutch pack
#2 Wet PTO clutch pack
#3 control valve and actuator
#4 break down of control valve