There was a good story about a shortline's experience with those CAT-engined units on Loconotes a little while ago.
Essentially, they gave good service as long as you religiously followed the maintenance regulations, which include changing the engine oil regularly. This shortline was later bought out by RailAmerica, who cut back on maintenance to save money. The CAT engines responded by having crankcase explosions, and RailAmerica's response was to prohibit employees from using the locomotive side walkways when the engine was revved higher than notch 3, or something like that, before eventually getting rid of those units.
EMD and GE engines are far more tolerant of poor maintenance practices.