First off, I'll assume your 300E has the M103 motor.

My 126 car also has an M103 motor.

I needed a new alternator last September and instead of replacing with the 80amp Bosch AL66X - 80 amp, I installed an AL166X - 100 amp alternator which is supposedly for diesels. My 103 likes it just fine. I see 14.30 volts at first start-up in the am. Never saw that with an 80amp alternator. The AL166X fit exactly as the original alternator that was replaced.

I'm not saying this will fit your application, just sharing information.

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