If you are going to be in this business you need to know how to work on everything you have. First step would be buying a pump that doesn't have to be rebuilt. Saves time and money in the long run.
Generals are garbage. I have 7 Udors. Some are 6 years old. None have ever been opened. Udor ran their GKC series pump for 8 hours without water during testing and lost 20% effeciency. Run a general or AR like that and see what happens. I was rebuilding generals every six months when I started like everyone else until I found Udor.