Well, I've been looking around our little town for an appropriate coolant for the K1100. A few parts stores and Walmart are my choices. Car Quest and Napa could not tell me if any of their coolants were indeed Phosphate and Silicate/Borite free. While Prestone Long-life used to be recommended, and may be fine, their "new" extended life formula does not specifically say what is not in it either. They hedge on their website, but they basically say phosphate only matters in Europe, and that all US coolants contain phosphates. That leads me to believe that theirs does also.
Finally, at of all places, O'Reilly's, their house brand long-life coolant said all the right things. Good for all engines, good for aluminum engines, can be mixed with all brands and, phosphate and silicate free. So, I bought a gallon of that and a gallon of distilled water. I'm sure it will be fine, but O'Reilly's? Never would have thought it.