Ours was a fuel line fitting/washer combination into the injector pump on a 8.3 liter 300-hp Cummins, Alison 6 in a 1999 Newmar DutchStar with 58,000 mi. We stopped for fuel and a fellow (who works for Cat) pulled up and said we were spraying fuel out the back. We got towed to Diesel Injection Service in Windsor, WI who said the problem is a documented one with this pump/engine and there is an upgrade fitting/washer combination. Parts were less than $100 but the labor (it was tough to get to) and the steam cleaning was another $600. Incidentally, that fitting/washer is a one-time use. Remove it and replace the same one and it leaks twice as bad!