OK, you’re going to really hate this, but go with the external starter and be done with it. We went through the same issues. Ours were always broken brushes or weak batteries. It’s a fine little 2 stroke motor, but the starter system just sucks!!!
We have two which we road race. A MY07 and a MY09 and they both would randomly go through the same problems. When we’re on the grid and the flag goes up, they MUST start! At this point all the starting components are in place, but the starters aren’t even plugged into the harness. And they really couldn’t care less how charged the battery is!
For $250 you can get a brand new Coleman with battery from any kart supply house or vendor, and it will start your Leopard EVERY time.
It’s just not worth the nonsense. Been there, done that!!! Like I said, great little motor, but I hate the starter!!!