seriously...can you stop trying to solve a problem you don't have ?
you got a used car, that you said has full service records and is in good shape. Enjoy it, instead of trying to fix something that isn't broken
I presume your car runs? I presume it isn't billowing endless amounts of grey/blue or black smoke out of the exhaust while it idles or while under WOT? I presume it isn't eating a quart of oil every time you run a few errands? I presume it doesn't take endless cranking cycles to start the car? If you answered no to the above, you don't have sludge, don't have a stuck ring, and none of this stuff you are tossing in, or thinking about tossing in, will do a thing except waste your time and lighten your wallet. Stop trying to McGyver your car and just enjoy it, and stay up to date on the scheduled maintenance per the service manual
They mean flush your engine with diesel oil to help break up oil sludge. It's a stupid idea with an old engine, since it'll probably just make the sludge move elsewhere and clog. Just drive the car and keep up with oil changes.