Went to my Marine diesel shop that supplies me with parts and found out that they no longer carry Shell ELC coolant. They are an authorized repair shop and distributor for multiple marine diesel engines including John Deere, Volvo, Cat, Yanmar, and SCANIA. Apparently Scania has found that Fleetguard OAT is the superior coolant. They tested them all and found that the others have been pitting the interiors of their cooling systems. Shell ELC was the worst by far. Not sure if this is specific to marine diesels, but I will be running Fleetguard OAT in my $25k Yanmar engine exclusively and will be promptly flushing the Zerex out of my Powerstroke and filling it with the same.