It sounds like you over tightened the pinch bolt and cracked the aluminum cassette? You only want to snug those but use some loctite so they don’t back out (unless it’s a bolt and nyloc nut). Put everything together loose, slide the axle through, snug the pinch bolt then tighten the three cassette bolts to the frame hanger.
Don’t feel bad some of these kart components are poorly designed and made of crap metal. Yes, the bolt pattern is generally universal but be careful what you’re buying. The best stuff is made from 7075-T6 but some are made from easy cutting screw machine stock.
FAA certified jet engine and aircraft technician,
Nicholson Speedway class champion 2001,
Yamaha KT100 Service Center,
41 years karting experience