Yamaha YFZ450 motors

Good morning, I am new to the forum. I'm 75 years old and love getting ATVs back to usable condition. I particularly like the 2006-2009 Arctic Cat 250 Utility. I currently own 6. The 2006 I am working on only has reverse and low gear. The "drive shaft" in the transmission is completely stripped where the high gear would mesh. Has anyone on here replaced the shaft. I'm told I have to split the case. I was hoping that someone on here could let me know how hard it will be. I already have it stripped down to where the shaft coming in from the clutch side is the only thing left. I was hoping I could just remove the driven clutch and drive it out from there. Directions say different. Any help would be greatly appreciated.

Which is more reliable? Shaft or chain drive? 

Do any have any experience replacing 2001 Big Bear 400 Front Differential Input Shaft bearing and seal. Getting ready to buy one but the seal and bearing are bad. Any help would be appreciated. 
 
 

I hadn't driven my Kodiak for a two months, and since it was low on fuel, the first thing I did was filled it up to maybe 7/8 full. Getting ready to start it, I rotated the fuel selector switch to "on" and within seconds I smelled and saw fuel dripping onto the floor. I quickly turned it off and the fuel gradually stopped - I can repeat this.
The fuel is flowing from the hose that is connected to the bottom of the carb, and routes around to the left side toward the wheel well. Any idea what's going on here? It ran fine the last time I had it out.
Thanks...

Hey guys, I just picked up this quad that hasn't run an a few years. It is missing the front drive shaft. Does anyone have the can measure for me or know of a replacement? If I can get the dimensions I can try to use one from another machine. Thanks!