Old thread here from 2000. FWIW
http://www.peachparts.com/shopforum/performance-paddock/1330-m103-engine%3B-good-garbage.html

My 88 300CE (m103.098) had the head gasket replaced by the previous owner in 2001 with 41k on the odo as a condition of purchase. Now it has 146,000. Still have the same head gasket. It weeps a bit at the rear of the block. My indy shrugs it off. Oil consumption deteriorated to a qt. per 1000 mi. Had the valve stem seals replaced at 75k. Problem solved. Now it burns less than 1 qt. before I change the oil at 3k interval.
Water pump went at about 100,000. I just replaced the fuel pump relay for the second time. Other than that, I've had no problem with the motor or ignition.

I've always followed the MB dealer in this area and used 5W30 motor oil and MB recommended antifreeze.
Runs and looks great for a 28 yr old car.

Had a '91 190E 2.6 before the CE. No problem with that engine either.