diesel don,

I believe this is a "normal" wear event after several hundred thousand miles, or some very high number of starting cycles. The engine stops when you shut it off with the crank in one of four positions, which correspond to one of the four pistons approaching top dead center on the compression stroke that stopped the engine. In reality the number of positions may be less as wear causes one or two positions to be favored (a little higher compression increases the chances that piston will be the one that stops the crank than another piston in a cylinder where there is slightly less compression). So, as the car gets older the ring gear teeth that are used in the initial engagement and application of torque get fatigued faster than the rest of the ring's teeth and consequently get worn off or break off. So, what you have is not normal for a car with low miles, but for something with high mileage, it is probably more common than not. If the starter motor bendix or the pinion gear has some worn features that prevent the easy, full engagement of the pinion on the ring gear, the problem is likely to happen sooner.

On my car I did the clutch at the same time, even though at about 185,000 miles it showed about 60% of its original thickness remained on the disc, and the throwout bearing. Getting to the ring gear or clutch mechanicals is the same task and is much more than half the trouble.

Hope this helps, Jim

__________________
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)