I have an '05 C15 Acert in a T2000 KW here. Known problems on that engine are IVA error codes (often low oil psi warnings). The IVA housings have been known to get ripped right off the head due to weak mounting points. When this happens you have chunks of loose metal floating around in your valve train which will wreck your cam and put a window in your cylinder head. Been there done this $13,000. There was a recall. Any Cathouse can tell you if the upgrade to rocker studs has been done.
Also chronic error codes involving the IVA and IVA sensors. The sensor like to see a certain oil PSI of it will derate the engine. Common fix was to lower the PSI requirement in the ECM using the laptop and software. IVA issues can also be casued by worn out wiring harnesses.
Our Acert was reliable after replacing both harnesses and doing the uograde mentioned above. There is TONS of info on this at TTR. do a search