firemanjim
Just kartin' around....
Let me go hunt down my manual for the 125cc I bought last year. I'm not sure about the other plug. Can't say if I've ever had to remove it..... BUT my brain is telling me it's probably the trans detent rod-thingermabob..... You know, like in your car. It is a spring loaded locating pin, basically... BUT let me go look in that manual. It's in my sock drawer..... 
I'll be right back....
EDIT
Immm bAaack..... Well
! The manual that came with my engine will do us no good.... It is all in chinese..... BUT looking at the drawings therein, I did see that the bolt in question is indeed by the trans and is also located near the shifter shaft. Almost POSITIVE its a trans detent..... You know when you shift, and you feel it "click" into gear? It's the detent that is falling into each dimple, making that click feel/sound. Make sure your trans still shifts correctly. If not, you might have dropped another piece, that you didn't see..... 
I'll be right back....
EDIT
Immm bAaack..... Well
! The manual that came with my engine will do us no good.... It is all in chinese..... BUT looking at the drawings therein, I did see that the bolt in question is indeed by the trans and is also located near the shifter shaft. Almost POSITIVE its a trans detent..... You know when you shift, and you feel it "click" into gear? It's the detent that is falling into each dimple, making that click feel/sound. Make sure your trans still shifts correctly. If not, you might have dropped another piece, that you didn't see..... 
......
