Check your options too as I think some of these had brushes that could be replaced and only cost about 3.00 or soemthing like that.
I could be wrong but would sure beat a new alternator.

As for bigger is better? It's really a matter of application. If you do a lot of short hop night driving then yes, the bigger alternator is best for you. I doubt you tow with your MB so you don't have that extra draw from a trailer to worry about so personally, I think for the extra money I would just stay with the original alternator.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique