Murcury,Mechanic?

Ive been having a problem with a 92 Murcury Topaz as it wont shift out of first gear, I pulled the trans pan off and found a plastic gear laying in the pan, name of gear? I figured Id have to at least pull the Cvaxle out inorder to to replace the gear and possibley the transmission? Ive found that that is a roll pin or a alen screw holding the spiderand side gears in place which would have to be removed in order to remove the CV axle. Question 1, name of broken gear. 2, roll pin or alen screw? 3, Does the transmission have to be removed inorder to replace the plastic gear?
Please E-Mail me at Dogrocksee@yahoo.com :banghead: