Just cleared up a headache of my own. After changing coolant, my 300SE had a miss in the #3 cylinder. Checked it five different ways and finally discovered by accident that the plug was bad. It's a Bosch Super H9DCO with less than 5,000 miles on it. Still can't figure if/what the coolant change had to do with it.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD