I just saw this post. I want to see if it can make 300,000 miles though. If you read his post, you'll see he had to replace his transmission at 90,000 miles because of a vibration going from 4th to 5th gear between 50-60MPH. I don't think it would've needed replacement if the fluid and filter had been changed at good intervals. I bet it's one of those newfangled "lifetime fill" transmissions. I figured out these "lifetime fill" transmissions long ago. It's a scam by MB to make you buy a transmission every couple of thousands of miles because "lifetime fill" makes you think the fluid never has to be changed.
http://www.mbworld.org/forums/showthread.php?p=1353541#post1353541

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

Yeah my grandam has a lifetime fill tranny too. Low maintenance is a key selling factor. You should see the maint schedule on my New Lesabre. Very little scheduled maintenance other than changing the oil. I really wish my grand am had a dipstick for the tranny

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My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory

The original post details the transmission issue.

My '97 E300D had a lifetime fill tranny. To my knowledge it never had a problem when I sold it at 236,000 miles. I'd say that's pretty good.

Scott

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Scott
1982 Mercedes 240D, 4 speed, 275,000
1988 Porsche 944 Turbo S (70,000)
1987 Porsche 911 Coupe 109,000 (sold)
1998 Mercedes E300 TurboDiesel 147,000 (sold)
1985 Mercedes 300D 227,000 (totaled by inattentive driver with no insurance!)
1997 Mercedes E300 Diesel 236,000 (sold)
1995 Ducati 900SS (sold)
1987 VW Jetta GLI 157,000 (sold)
1986 Camaro 125,000 (sold - P.O.S.)
1977 Corvette L82 125,000 (sold)
1965 Pontiac GTO 15,000 restored (sold)