Got it all open again, and it won't pop in place like it will on my spare transmission. I just don't get it. I KNOW this is the issue because I can see wear markings on the gear showing that its obviously slipping or not quite in the right place, but I cannot for whatever reason get it to slot in. I tried both gears, neither will lock in the groove. I then tested both GEARS in the SPARE transmission and BOTH lock in

so its something with the output shaft apparently. I tried knocking it in with a screwdriver and hammer in case it needed some harder persuasion and it still won't do it.
It seems like there is a spring clip or something where the gear slots into it...maybe its damaged or something, who knows.
Here is the SPARE transmission. You can see it "pops" in...but my wagon's doesn't do this. It just kinda sits in as far as it can, but never pops into the groove like shown below:
http://www.youtube.com/watch?v=XZziX4_BzJM&list=UUVPng-6Ys8Gr9402CRgWiOg&index=1&feature=plcp