The question of switching oil types is wallpapered with stories or personal anecdotes for and against. I use exclusively Mobil 1 synthetic oils in all my cars. Some, luckily, from very early in life, and some started on Mobil 1 synthetics well past 100,000 miles.

Oil usage for me comes in two distinct varieties. First there is oil that one way or another leaves the engine through the tailpipe, and then there is oil that leaves the engine and ends up on the ground or on the plastic lower enclosure under the engine on newer MB's. There are stories about how both can be aggravated by switching to synthetics. And there are stories about how the kind of usage that goes out the tailpipe can be reduced. I don't know of many, if any, stories about how synthetics reduced the sort of usage that results in oil leaking onto the pavement or lower engine enclosure parts.

As I have learned to view the problem of leaks, if synthetic oil results in more leakage it is because the synthetic oil dissolved some sludge that was "sealing" the spot. I also believe the synthetic oil removed sludge from other parts of the engine, where it added to the life of the parts. In the end, the leaks, if they become annoying, can be fixed by relatively simple maintenance. The 1988 300E we have is an exception. That car developed a leak between the head and the front of the chain box and required a new head gasket to be fixed. At about 180,000 miles it was time to rebuild the head anyway. That car went on synthetic oil at about the 100,000 mile mark and the oil leakage was more a result of a failure of the thermostat housing plastic hose connection to the radiator - and the subsequent overheating - than the change to synthetic oil.

Same with my 1983 240D. Delvac 1 from ~ 140k miles. No oil leaks yet. And no significant oil consumption - about a quart every 8,000 miles. So, when it is low, I change it.

I use Delvac 1 on all my cars (it is rated for spark ignition engines as well as compression ignition engines). In the past, when I began using it, it revived my 1982 240D for several years - that car already had a rear crankshaft seal leak that my son ignored at college and ended up running it dry, killing the engine with 300,000 plus miles on it - actually cleaning the accumulated internal junk out of the engine to the point where the compression increased and the low temperature starting performance improved to make it reliable in the Troy, NY winters.

My point is that there are all kinds of cars in all kinds of conditions. My view of one that is being held together by dirt is that it is not reliable, and there is nothing worse in my personal experience than giving my wife an unreliable car to drive. Or my daughter. Or my sons since my wife will make that my problem in the end. So, I don't believe internal engine consumption is likely to go up, and if there are more leaks through mechanical joints, well, if you want the car to last a long time and be reliable, fix the leaks and use synthetic oil. Not that my beliefs on the subject are of any greater value than anyone else's, but you asked.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)