Hey guys, I am surprised to hear you have difficulty in snow with the W123 Diesels. I have driven my 1971 (W115) 220D and 1975 (W115) and 1982 240D's all over the Northeast, and up to Alaska and back. I also ski with my family quite a bit, and have never had anything but great experiences in snow and ice with these cars.
They all had/have manual transmissions, which may have something to do with the results I have had, and I always use 4 season Michelin "H" rated tires (195/70HR-14 MXV's presently and for the last 6 years or more) which may also help. But I can say I have never been stuck so I could not get out, and I have passed or crawled around other cars in snow and ice storms that have closed roads.
I did learn in Alaska that you put the clutch in before you lift the accelerator, as the rear wheels will lose traction and run at idle speed almost instantly in really icy conditions going downhill due to the compression braking of the engine. The effect is a lot like applying the emergency brake, and the rear end will quickly pass the front end. Other than that, I have only great things to say about the car in snow or ice, or rain or any combination of them.
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
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)