If my math is right, you have about 440,000 miles on the motor.

I'd wonder about the condition of valve guides/seals. When these wear, oil gets thru to the spark plugs. If this is indeed the case, the car can run rough until warm as the oil that's settled on the plugs has to be "burnt" off by the secondary side of the coil.

The 103 motor seems to guise oil consumption fairly well, so taking a plug reading may not tell you as much as you'd think.

If your oil consumption is high, I'd suspect weak valve stem seals or valve guides.

Just another opinion.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"