what an interesting discussion.
i think that i shall offer you another perspective.
until 7years ago, i never used a multi-grade oil.
my first benz was a 1973 220. was the original owner. ran it for 3 years and 140,000 hard, fast miles in texas. from christmas to easter i ran a valvoline 30 wt racing grade, for the rest of the year a valvoline 40 wt racing grade.
changed oil every 3,500 - 5,000 miles. never noticed any significant oil consumption for that 4-banger.
replaced it with a 1976 450sel. ran the same oils the same way. traded it at over 200,000 miles in 1985 for one of the first 300e's. engine never experienced any significant lube oil consumption. replaced the timing chain at 120,000 miles. no other engine work.
hated the 300e, traded it for a 1986 560sel. ran the same oils. no significant oil consumption. then my old mechanic expired and my new one was devoted to multi-grade oils. it was probably normal wear and tear, but within 20,000 miles on multi-grade stuff, this engine began to experience significant consumption. principally down the valve guides. so at 220,000 miles heads were pulled. what a nice looking engine in most aspects. cylinder 2 left exhibited some scuffing in the top ring reversal area but all the rest were virtually as new. camshaft lobes exhibited some wear. at this stage, engine was consuming 1 qt per 500 miles, and it went to this level fast: had been 1 qt per 3,000 miles and then instant consumption of oil. piston crowns were beautiful - perfectly clean.
cams replaced, valves replaced, guides replaced, timing chain replaced.
since this upper end renovation, engine is tight. no oil consumed between 3,500 - 5,000 change intervals with the multigrade. only complaint that i have is that the hydraulic lifters take too long to pump up in the morning at 30 sec-120sec idle.
that is my last benz that ever ran on a single wt lube. all my others have always been subjected to the multigrade philosophy. my 1987 560sec, i am the second owner, was always subjected to manhattan benz and multi-grade. had to renovate the top end at 65,000 miles. piston crowns were covered in gummy lube deposts. valve guides and valve stems in deep trouble. camshafts with more wear than my 560sel at 220,000 miles. po had oil changed every 3,000 miles according to the service records. my guess is that the engine was never run. after all, 42,000 miles in 13 years.
anyway, since top end renovation, engine is tight and no significant lube consumption over the last 15,000 miles. and no lifter clatter at start-up. but the oil pressure gage does drop to very low levels when the engine is warm and idling.
picks up into the normal range when the revs increase.
my 1995 e320 cab is so young, 10,000 miles, that it remains tight and quiet and leak-free after all this time on multi-grade oils.
all oils used are mineral.
my conclusion is that i am not sure that i can find any reasons against using a single wt oil for a hard driven benz in southeast, south central texas.
but i am all ears to other pov's.