300sd2000,

The symptoms you describe reflect a starter motor that is aging and suffering from poor insulation resistance. Lots of words for you need a Bosch rebuilt starter. I highly recommend the Fastlane units.

As an electric motor ages, and Diesels are particularly difficult on starters, the insulation on the wires that the battery current flows through loses it's ability to resist current flowing through the insulation to an adjacent wire or the metal structure of the motor, which is grounded. Insulation resistance is adversely affected by temperature, so, when the unit gets hot from ambient temperatures, or, underhood temps after running when it is hot out, a weak insulation can begin to significantly leak current whereas the same unit will perform ok when it is cold. So, with a short in the starter it is no wonder your voltage droops so severely.

A rebuilt starter from a local rebuilder will normally have all of the replaceable mechanical parts replaced. They will sometimes have all the replaceable electrical components (voltage regulator, your capacitor that failed, and, if the guy is really thorough, the diodes in the rectifier) replaced too. But they will almost never rewind the machine. So, the real problem is not fixed. Since this procedure is usually adequate for gas cars (their starters don't see nearly the abuse a Diesel starter sees) it is accepted as the norm for most rebuild shops.

The rebuilds by Bosch include insulation restoration and the machines are really in like new condition. The ones from Fastlane are very favorably priced and you get them really quick. Changing them out can be a chore though. If you do it yourself, disconnect the battery! I have personal experience that I will never forget on the subject. Good luck, and I 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)