Spoiled Christmas….What did I do?????

Good morning all. I hope everyone had great Christmas. For Christmas I decided to modify my boys 2010 170. Snorkled the CVT, air intake with uni filter, rejeted carb, 23 inch ambush tires with 12" ss wheels, and new shocks. The boys were super excited and we worked on it together for about 4 hours. Got it all done and it looked awesome!
Kids were having a blast showing it off to their friends. When the family started showing up and the boys could really show it off that’s when things went bad. My son was taking his cousin for a ride. About 10 minutes later they came walking home. "Dad I was just driving and I heard the chain come off". When he got out to check on it he noticed transmission fluid leaking. There is a large crack in the case towards the bottom. Transmission is done and the boys a really bummed… 🙁
So, did I really mess up by doing these mods? Did I do something wrong?
They got about twos hours of use out of it before it came apart. I snorkeled the cvt with 1 1/2" pool hose. Do you think the transmission was on its last leg and with the bigger tires it just put it out of its misery? I know that sometimes they would have a hard time getting it to go in forward gear. They would put it in forward and have to give it a little gas, it would make a little grinding noise (if you can’t find it grind it type of noise) then it would slip into gear. Was that a sign of bad things to come?
How much is one of these things to replace? Does it just unbolt and built back on? I am a weekend warrior, not a mechanic by no means, so I don’t think rebuilding it is an option for me. Can I take it off and have it rebuilt? If I replace it how long will the new one last with these big tires on it?
Sorry for such a long post, just have lots of questions. Thank you all in advance for any advice!!!
D

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