Help trouble shooting why the shifter sticks when shifting into 3rd gear

i have an 83 gt celica and i am have trouble getting the gear shift to go into 3rd gear. I can do it if i shift slowly, but doing this fast risks shifting into 1st or getting jammed between 1st and 3rd.

i have attached a link to a diagram of the shifter parts and this contains more info on the car and engine type if needed.
My question is what exactly do i need to replace to make it easier to shift?I have removed the boot and the gasket just to look inside and see if something looks bent, but I have not taken out the retainer or the plate below, but i am thinking that is the piece i need to replace. any help would be welcome.

http://www.villagetoyotaparts.com/showAssembly.aspx?ukey_assembly=346802&ukey_make=1021&ukey_model=14406&modelYear=1983&ukey_driveLine=6069&ukey_trimLevel=14018&searchString=shifter

My guess is that the problem lies in the shift linkage inside the transmission body. A bushing has worn out or or connecting rod has become bent from the constant shoving...or combination thereof.

You would at least need to remove the ball socket that the shifter's ball end connects into to see what might be the problem.

Good luck!

The bushing and another part not in the diagram are typical causes.
The other part is a rubber seat that goes into retainer in the diagram.
The larger 'ball' part of the shift lever sits in that.