My '82 auto 240D gets 28-29.
Do check your odometer. They have a nasty habit of slipping. It affects both the trip and overall odometer, but not the speedo. There are many threads that address this issue, but simply put, the metal gear slips on the shaft. It was originally a press fit, but over time they looesen up. Repair involves removing the speedometer from the car and deforming the shaft a little so that the gear no longer slips.