I'm no mechanic or CEO, but.... Based off of my observations of our real-life 2000 TC2000 FE Cummins (bus 25), I would replace 10001. Bus 25 seems to be the bus with the most downtime in the whole fleet. I think it had its engine replaced a while ago (maybe the same issue as 10001 :D), and it just doesn't perform as well as its twin, bus 24. It runs fine, just not the same and a lot of downtime.