TL90 Weak Pto

Weak pto power. Changed hydraulic filters, measuring 180psi going into pto clutch assy. to lock it up. Should it be higher? What should the pressure be? I have read should be as high as 275 psi? Could the pressure be low because the clutch pack is leaking by, seems like that could be possible, but where can I measure the available low pressure (250-300 psi)? I follow the lines but can not identify where the incoming low pressure supply line is. Hate to rip out the pto clutch pack if not needed, tractor only has 1300 hrs.Any info anybody has would be greatly appreciated. Thanks!