Modulator just has an O ring. I hope everything is well now. Make sure you do not have throttle shaft seals leaking on the injection pump. That can make it appear to be the rear main seal also. The leaking fuel washes it's way down the valley and the rear of the engine and appears black like oil from the crud it picked up along the flow route. Like I mentioned the leaks are never ending at this age and nothing short of changing all seals and gaskets will make it better. I said better. Nothing is infallible. Good Luck. Happy for you. My main concern was that my hose was not the issue. Looks like contaminated fuel has been the root of the problem. Major truck stops sell the best clean fuel, and diesel sitting around in jerry cans condenses and make moisture. Drive on. I knew the tailpipe was short to life.