I'm thinking the problem is condensation of crankcase oil vapors on cold intake valves. EGR should help to warm the valves and carry no oil (unless the rings are worn out) and should not contribute to carbon build up. The 2015 ML quick warm-up mods (very rich to heat the cats and electric thermostats) are probably the MB response as they may warm the intake valves sooner to avoid condensation.
PCV was mandated in 1961. According to Wikipedia, older cars and modern off-road vehicles use a road draft tube which would have to be added after removing the PCV:
"The first refinement in crankcase ventilation was the road draft tube, which is a pipe running from a high location contiguous to the crankcase (such as the side of the engine block, or the valve cover on an overhead valve engine) down to an open end facing down and located in the vehicle's slipstream. When the vehicle is moving, airflow across the open end of the tube creates a draft that pulls gases out of the crankcase. The high location of the engine end of the pipe minimizes liquid oil loss. An air inlet path to the crankcase, called the breather and often incorporated into the oil filler cap, meant that when a draft was generated at the tube, fresh air swept through the crankcase to clear out the blow-by gases." I remember those and could fabricate and install one or two in a couple hours.