Oh yes I have made sure it's clear of any obstructionHave you looked under the seat where the lever attaches to the 3 point top plate and see if anything is jammed up there or debris keeping it from moving?
It is my father in laws tractor and it has been like this since I started working on it .Use some penetrating spray and spray the area where the round rod comes into the tractor case. Spray the area where there are washers and nut holding the lever to the rod into the tractor with a lubricant.
I would assume that area is corroded but did this problem come up suddenly or over time? If it was suddenly then probably a bad assumption on my part.