Miles81_240D,

Congratulations on a great decision and a great buy! The answers to your questions above are pretty complete, so I won't repeat any. The transmissions in these cars seem bullet proof to me, as I have never worn out a clutch and have never, ever, taken anything on the transmission apart for any reason. I, like Larry, have driven these cars many hundreds of thousands of miles. The whirring or rolling noise you hear may, or most likey may not, be associated with the transmission. These cars have a driveshaft center support bearing that is mounted in a bracket that has a bonded rubber donut around the OD of the bearing and ID of the bracket. As the rubber ages and dies, it cracks and eventually the bearing starts making enough noise that the damaged isolation of the rubber donut can no longer manage, and you hear the bearing going bad. There are some other items in the drivetrain that can make noises too, but it is unlikely it is the transmission.

Changing the oil in the transmission and differential will give you an opportunity to examine the whole drive train to see what is up, and the chances are the existing oil is due for a change anyway. Both units have a 14mm Allen head hex screw that plugs the fill (on the passenger side, about half way up the transmission and differential housings) and the drain opennings. I believe they are pipe threads or some tapered thread arrangement, so I end up tapping the Allen wrench with a hammer to break them loose and to tighten them so they don't fall out. Like others I use synthetic oils here (and in the engine), and I do not use ATF in the manual transmission. I have had good experiences with a RedLine Oil Company product, a special formulation for manual transmissions and another product for differentials. This stuff costs twice as much as other oils but lasts and gives good, smooth shifting characteristics. Any good quality oil will likely do the same though.

Enjoy your new car, for many, many miles! Good luck, 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)