The recent book Southern Pacific & The KM Hydraulics by Robert Zenk dispels many of the stories concerning the life & death of these unique ( for the U.S. ) mainline diesel - hydraulics.
The maintenance & reliability issues were mainly with the Maybach diesels and the original KM design for the cooling radiators. The high revving Maybach V-16 engines were very precise machines, as was to be expected with German designs. One Espee mechanic was quoted as saying: " I've never seen so many fluid filters on a prime mover before." ( At least not until the Sulzers showed up !!! ) The original design for engine intake air was also a big issue, resulting in burnt cylinder heads and fuel injector nozzles. The engine air intakes on the carbody units had to be relocated to be lower on the carbodies. As well, the radiators were redesigned on the hood units for better cooling in tunnels and snowsheds. ( Sound familiar ??? ) The need for 2 prime movers per locomotive to achieve the desired horsepower rating was also a complicating issue, as it was with U.S. Diesel - Electric locomotives as well. Recall that Espee favored Alco PA's over EMD E - Units for this same reason. Espee mechanics in Roseville were used to EMD's rugged F-Units; anything else was viewed as foreign.
By contrast, the hydraulic transmissions and drive lines were very reliable, with only a very few cardan shaft failures reported. Having all 3 axles on a truck joined together virtually eliminated wheelslip, as all 3 axles would have to be slipping at the same time.