Flushing your engine might be a good idea at 100,000 miles. Just realize, diesel gasoline is a harsh chemical that eats away at gaskets and oil seals, as well as the oil sludge you're trying to remove. If you add enough diesel and let it soak for a long enough period it will eventually dissolve all those black, tarry deposits clogging your oil passages. At the same time, it will eat away at rubber.
So be safe. If you've never flushed an engine before, why not buy a safe commercial brand and follow the directions printed on the label? Usually, the only cars that need their engines flushed are ones that have not been properly maintained with regular oil changes. I regularly flush the Saturn featured in this video yet, for all the flushes I've done, this vehicle has never needed new oil seals or gaskets.
