Brett,
I have a 1998 National Tradewinds with a 3126 CAT engine with 2 fuel filters and a hand primer pump. In talking to a mechanic the other day I was told to fill the fuel filters with ATF (Automatic Transmission Fluid) instead of diesel. He said it was a little thicker, the red color would show up better if there is a small leak in the fuel line, would clean the injectors and that a lot of truckers put a quart or so in their fuel when they filled their tanks. Have you ever heard of this and what is your recommendation?