benzat,

The symptoms should be belt squealing, and possibly a lower than usual engine idle speed. As the condition develops, it usually becomes fatal (for the alternator) very quickly, as the added load in the bearings quickly causes them to get hot, which adds load, making them hotter, and so on. If it gets hot enough, the bearing material melts, and that leads to a seized shaft pretty quickly. The old alternator should have been difficult to turn by hand after the belt was removed or after it came out. 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)