Jerry, as Gary said a thourough inspection should be performed of both Prevost and converter installed systems. As for replacement, I generally depend on the outcome of the inspection and life expectancy of the serviable items. Air bags, if original, likely should be replaced. However, the blue or green silicon hoses probably only need replaced if visable signs of wear are discovered. Some also suggest replacing the brake diaphrams, or whatever hey are caled, and the Norgren air valves. Of course, if you have an open checkbook, it never hurts to replace more than less.