Is this machine still under warranty? If so, I would not let the dealer tell you that there isn't anything else they can do. If it is under warranty, it is thier responsibility to fix it period. If it is not under warranty, then I would say your friend is right, you cannot tell if a sealed bearing is bad just by looking at it unless it is completely wasted and comes apart. If there is a bearing that is so bad that it allows enough movement to damage gears, then I suppose a bearing problem is a possibility. However, if your problem is a bad bearing or two, and the dealer techs couldn't figure that out, then someone needs to be hit in the head with a big ass hammer. I am also wondering if the damaged gear in the t case is even related to the noise that you hear only when turning right? That seems more like a diff or axle bearing issue, I don't see how the two could be related. I think you have two different problems.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.