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Aluminum has turned black just behind pump

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I own a 2008 Subaru Legacy from new now with close to 110k miles.

My radiator failed recently leaking in the the plastic aluminum joint of the upper tank.


I decided to do the timing belt, crank seal, water pump, bearings replacement for the first time now that I removed the radiator.


Back in 2009 a flying object damaged the radiator and was fixed by Subaru dealer. They repaired the radiator and refilled with non subaru coolant, it was replaced with another brand back at that time.

After a few years I did myself a coolant fluid replacement using a SUBARU cooling fluid and Cooling System Conditioner SOA635071. That was done more than 5 years ago.



Now that I´m doing the timing belt I removed the water pump and found a black color in the aluminum of the cooling port instead of shiny aluminum as I´ve seen in multiple youtu videos showing the waterpump replacement.


The coolant I removed looks very dark after after poured into a plastic container. I would say there is no oil in the fluid but it is very dark in color.


What can turn the aluminum black in the ports like this? i hope the attached picture works.


I will install a brand new mishimoto radiator to replace the oem radiator.

My main concern is should i try to clean the ports somehow back to aluminum shiny color before assembling all back together?


I have also noticed the subaru conditioned SOA635071 has been discontinued, is this correct?

I do have conditioner in stock with subaru coolant. Should I use the conditioner now with mishimoto aluminum radiator?


Should I go ahead and remove engine and redo head gaskets now to investigate more into this black coloration of the aluminum?


thanks for any advice


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