My 3720 has 3000 hours. I’ve only had for few months. I used tiller and brush hog recently with no issues. I added a 3rd function valve and when finished pto will not work. Light on panel will come on when activating switch but nothing else. I’m getting power to the pto solenoid, and I’ve replaced the solenoid. Also pulled solenoid and block to inspect. All clean, no gum. The lever to move between mid and rear pto will only move about 1/4”. That seems odd, minimal movement. I can fill one detent when moving lever by hand and the panel light will move between rear and mid pto when activating switch. It has fluid. When activating pto switch you can not turn pto by hand. When not on, you can turn about half turn before hitting something internal and stopping (both directions). I also tried bypassing the 3rd functioning valve since it is coincidental that is when it stopped working. I bypassed by connecting hoses by new valve, not by putting the old tube back on. I’m tempted to put old tube back on. One thing to add. I could not get the plastic cover under the seat off, it seemed to be jammed on something. Could something have come unplugged while trying to get that cover off that is related? Any ideas are welcome.