someone on the list mentioned the use of MACS13, and i recall them saying its also at NAPA stores. i have located a product at a NAPA store (called NAPA Number 13, stock number 1300), and wanted to verify that it is actually a radiator flush / rust inhibitor product. its darn cheap ($1.60 for 8 ounces) so i'm hoping this is the stuff...... please let me know. thanks. PJ