something after you check the fluid would be the shifter "balls" there are two ball bearing type balls that the shift rod rides on, going into the tranny, they are pressured by a spring, sometimes the springs wear out causing the shift rod to have a little play, up and down and shifts get sloppy and dont want to go.

also my shift rod was bent, not that i shift my car hard or anything( i would NEVER do that:sarcasm)

or last but not leats synchros, go to gearspeed on the internet and order them, they are pretty cheap