400ex oil leaking out of the pipes

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.

Guys, I've got a 1999 Honda Foreman 450S.  It runs great, but smokes out the exhaust after startup until it warms up.  I'm thinking the valve seals are leaking.  I was wondering if there is a way to replace them without removing the head or if there's an oil additive that will recondition the rubber seals.  Any advice?

Which is more reliable? Shaft or chain drive? 

When you and a group of friends decide you want to take a long group trip of camping/riding/overlanding, how far are you willing to drive for your trip? Right now, i find it really difficult to want to drive more than 2-3 hours one way. 

I pulled out my Big Bear needed to do a few things probably havent been started in a year. Gassed it up charged the battery started right up. I have been using it around the property for this and that. Went to hook up my trailer to pull up to the house while it was idling it quit. Went to start it turned over but wouldnt start. After trying a few more times lost all power. Pulled it up to the house with the John Deere, the first thing i checked was the Universal fit soloenoil from Amazon and it was only a 10 AMP fuse so it does not universally fit the big bear it should be 30 AMP fuse. At the time i remember noticing it but forgot, at the time i had other problems like wiring harness being in a box stuck engine and no spark. when i bought it, yeah i know, thats one ishould have walked away from, but if i go to the trouble of hooking up my trailer and going there, its following me home.
Thats old news, i still need to check it all out see if it lost spark and see if the starter shorted out it was acting kind of sluggish, i replaced the fuse with the spare 10 amp and blew immediately. I will try a 30 and see what happens.