EDITED:
He said he could engage the PTO with the clutch just fine. When he tries to disengage the PTO , using the clutch it doesn't release. Sounds like a clutch malfunction to me.
I went to
AGCO Parts Books and looked up the clutch assembly on a MF 65. No hydraulics involved here. Purely mechanical as I thought. There are clutch levers that the throwout bearing is probably hanging in. The OP didn't mention whether it's a single or duel stage clutch. The single stage clutch is somewhat simple design. The duel stage has quite a few additional parts that if came loose could cause this hangup. Inspecting the clutch thru it travel via inspection plate would be my first coarse of action.