Ummm.... why would you even bother trying to degrease the cams? They're sprayed with oil when the engine's running. Leave the cams alone.
Clean the valve covers with anything aluminum safe (degreaser is fine), wash thoroughly and dry thoroughly before reinstalling.
You mention scoring on the cams, post pics.
The oil cooler and IC do not use coolant... if they're getting wet with it it's coming from the overflow tank or a leak in the rad.
Dark coolant is usually the result of rust. Sometimes it's due to other contamination such as oil but that usually separates enough that you can tell it's oil beading up on the top of the coolant. Clean out the system and replace the coolant. Check oil for signs of coolant and look under the oil cap for light brown sludge.
The shop servicing the turbo should check the wastegate and actuator.
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