GottaDiesel,

Check Fastlane by going to the on-line catalog and punching in your car's model and year. They tell you which cap to use and apparently the original cap has been superceded by one rated at a higher pressure for the W124, but they have some original parts in stock or can get them. I do not think it makes a big difference unless the pressure setting is too low, and the coolant is released when the engine temperature gets near the red zone. So, buy either the 1.2 bar setting cap or the 1.4 bar setting cap. Good luck, 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)