The "supercharger I referred to was the Mosselman unit - I understand they make both turbos and superchargers. I would by a 400/420 or 500 before I did a supercharger on a 300E.
On your auto trans, I understand (correct me folks if I'm wrong) that the auto was designed to be shifted manually when desired. I occasionally downshift with mine, and occasionally at a stop light I will put it in the "first" position for a moment and then back into "drive" while the stop light is still red. This 'tricks' the auto into starting in first gear without stomping on the gas. Sometimes I will up or down shift it through all 4 gears manually (watch your tach and the warning marks on the speedometer). No problems.
The rear axle ratio is the ratio of the final drive gears, and can be adjusted to improve acceleration, OR to improve economy (not both at the same time, unless you have an old Laycock de Normanville 2 speed rear axle. Boy, showed my age on that one!
)Changing your rear axle would be an expensive proposition as well. It sounds like you want more performance - so again I would just find a clean 400E or E420 in the w124 series.
On MB-Tex, Mercedes has a code plate on the metal strip in front of the radiator under the hood, with a lot of numbers on it, some of them 3 digit numbers. If you go to the site http://www.geocities.com/MotorCity/Speedway/5350/mbcodes.htm
the codes are explained (paint, upholstery, suspension, etc.), but basically a number in the 170's is MB-Tex upholstery. 171 for black, 172 for blue, etc. Leather was an option on early 300E's, standard on later ones. I personally prefer the MB-Tex as more durable in the long run, and less upkeep. The leather is supposed to be a little more comfortable, however.
Have a good New Millenium.
[Edited by JCE on 01-01-2001 at 12:35 PM]