Is any of this applicable to the 1989 300CE?
http://auto.consumerguide.com/auto/used/reviews/full/index.cfm/id/2205
Trouble Spots
Automatic transmission: The transmission may delay shifting into Drive or Reverse, and may be corrected by installing reformulated Mercedes-Benz transmission fluid. (1990)
Automatic transmission: Harsh and erratic shifts are often due to a damaged dust cover on the vacuum modulator for the transmission. (1990-94)