Repairs John Deer LX 255

My LX 255 runs, but when I pull out the PTO knob lately the clutch engages & then disengages. Only after I hold it
on for several seconds does it stay engaged. Yesterday I pulled the PTO knob out & I can not get it to engage.
Any ideas. TIA.
Jeff.

What type of PTO switch is it and does it has a reverse safety to keep the blades engaged when backing up? My LA175 has a round knob that I pull up to engage the blades. If I need to back up, I push a seperate button. If it has that type of setup, I'd suggest a new PTO switch. My 335 has a square knob/lever that I also pull up to engage the blades. However, to back up, I pull up on that square knob/lever again. If it has this type setup, it could be the switch again, but I'd check the reverse safety switch to make sure it's working properly.