buy the original MB trans fluid at $10-12 a quart. don't even try a cheaper alternative. it could spell disaster for your trans. I don't think your model year has a torque converter plug, it wouldn't hurt to check. mine had one (97e420) with same trans, it drained about 8 quarts if i remember correctly. make sure you change the filter and buy a pan gasket just in case the old one needs replacing. some recommend putting in a magnet because it doesn't have one. maybe some of the experienced tech could advice you on that.
P.S don't even think about those fluid exchange pumps that some chops use
good luck!