JonMark -
Part of this story reminds me of an embarassing situation I was in many years ago. While in high school, I was asked to drive the two daughters of our local Baptist minister, and some of their friends, to their band practice in the minister's car. The minister was out of town. The trip went fine, but on the way back, after letting the others off, I let one of the girls drive. I shouldn't have done it, but that went fine as well - no mishaps. A day or two later, when I visited my uncle (next door to the minister), the minister asked me some very embarassing questions. He was trying to figure out who had spun ruts in his lawn and peeled the retreads off his snow tires! It seems the young ladies had done some joy riding on their own after I left.
My point in telling this tale here is that someone else, kids likely, may have had access to your tractor during the time that your friend borrowed it, and they may have done the damage.
With regard to "splitting" a tractor in two to replace the clutch, that's standard procedure on a lot of tractor models. The way they are constructed, that's how they have to come apart. It's labor intensive, and best done by someone who has the right tools and has a clue what they are doing. Otherwise, it's no big deal.
Good luck on your repairs.