PTO lever locked up on farmall 230

Secondly the actual engagment happens as a result of a hollow shaft sliding on a solid shaft. That hollow shaft is designed so it actually only makes contact with the solid shaft at both ends. If you know or suspect the tractor was parked for extended period, years for example. Rust can build up during that non use as no oil gets up there during that non use. This applies to both sliding shaft as well as the detent.

Usually this is just a matter of removing PTO and doing a clean up. Find a spot to park tractor with front wheels about 1' below rears, then you don't need to drain the transmission. Just remove the bolts around the PTO housing and it will slide right out. If it has a belt pulley, best to remove that gear box first, keeps weight and balance a bit better. Don't misplace or loose shims between the two gear boxes.