How hard is it to replace the output shaft that the gear selector lever bolts to on a TH350 tranny? This is the keyed shaft that sticks out of the left side of the transmission. Mine is wore slightly so that there is some slop.

You must drop the pan and valve body to facilitate it's removal/installation. From my experience they all get a little play in them but it can be lessened by tightening the nut on the inside of the trans that holds this shaft in place and by replacing the seal.