I don't have much time here so I'll be quick:

Generally they're referred to as "oil makers" because the DPF regen is via a fuel dose on the exhaust stroke(s) and folks figure that IS the fuel they are measuring too much of in their used oil analysis reports.

Fuel system is HP and virtually anything not fuel will cause the HPFP to pretty much come apart and send all the little metal chunks throughout the fuel system.

Coolers, all of 'em. Radiator, EGR, etc. they are having repeat problems with them.

I gotta' go -- just thought I'd get something more out there to answer your Q