I would simply stick with the proven #10 Bosch for around $100. No worries about over pressure/flow rates and are well tested. And no modding of the plug and housing; P&P.
Thought I read where the higher pressure from the Johnsons were causing some leakage on some OEM coolers. But if you have Rudy's modded one then I say go ahead and push it.

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Mercedes Auxiliary Water Pump - Bosch (OEM) 0392022010 | FCP Euro