FME transmission, drive train and hydraulics are the big 3 for tracked vehicles. Wonder if they were supplied with spare fluids to take into the field. But 1/3rd going to depot isn’t that bad for two months of tactical use.
I don't have any specific knowledge other than what I've gleaned in reading about the breakdown rates in armored vehicles in offensives (and it's statistically predictable). I gather that this is the reason that most western armies have a "division-level repair yard" to deal with these issues. But as the PZH-2000 is not organic to Ukraine's armed forces, they're going to have to lean on whoever donated them. I don't know if Poland uses this tracked artillery system, but I'm sure that Germany would man a depot in Poland.