I have an 1800D that would mow for a while then the blades would start to slow and finally stop (PTO WOULD QUIT TURNING). After talking to several people who told me it was the PTO clutch I tore into the transmission and replaced the clutch plates and anything else that looked worn. Clutch plates were mostly worn out. Put it all back together with fresh UDT2 fluid and filter and it still does the same thing. Otherwise tractor runs great, good power, 4 wheel drive great, hitch lift strong. What else can I check?