Unfortunately the MB specified grease is pretty lame. These straps are continually being replaced because the grease they come with is not sufficiently water wash resistant, and rain water dribbling down inside the door causes the strap mechanism to rust and fail. I would look into a product we used in the Navy for mechanical devices exposed to seawater called Termaline 2. The lubrication duty required is not severe (meaning the speed and pressure of the sliding surfaces does not pose a serious challenge for the lubricant) but the environment seems to be. 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)