I posted these letters in the coolant recovery bottle thread, but I think they need to be in their own thread.
When I went through the documents that are in the coach from the first owner, I found these letters. They explain why 8 ounces of silicate was added to my coach in 2000 even though it was filled with Texaco ELC. It also may explain why when Cummins is contacted the engine serial number comes into play as to needing silicate. The important thing is this is a one time treatment.