I drive a school bus and we have cat and cummings engines. The cats by far are the better running engines but they do leak just like the cummins do. Most drivers like the cats because they run way better and acceleration is positive. Even the same size buses with the different engines, the cats perform better. We even have some john deere cng buses and talk about dogs!
The one thing with the cat that I have been told is that they are higher cost to repair vs the cummings, the one I currently drive has about 157000 on it and it runs very well. Only engine issue I have is the dash AC system but thats not the engines fault!