I cannot answer your question directly, but can provide with some info on the diode failure on my alternator a few months ago:

My S 500 L is factory equipped with the trunk fridge unit, which by the way provides a convertor to recharge the car directly from a regular 110V outlet.

Once using the charger, the diodes were damaged due to an electrical overcharge. The tech who repaired the alternator explained to me:

"The S 500s are equipped with three types of alternators, one for standard issued models, one for middly optioned models and one for fully optioned models, which in your case is the one fitted. This model your car uses is the same and only model fitted to the S 600."

He had to order the parts from Germany and when I asked him why could he just use the spares form a middly optioned S 500 alternator, he replied:

"W140s are extremely sensitive to electrical variations in their current supply, just a slight variation (less or more) can definitely damage all computer related systems in the short term". Interesting thought.

Hence, I would assume is not really advisable to switch to a higher amp rated alternator. I would have guessed that any other regular car would have benefit fron such an upgrade, but remember that the W140 is a unique beast.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]