I repeat, I would do 500 mile OIL changes, preferably with the Universal grade oil which is SUPER high detergent, high quality oil.
Rislone, the Lubro Moly treatments are basically SOLVENT, not LUBRICATING OIL.
Rislone was a very useful product in the days before engine oil evolved into the fabulous products that they now are. In the sixties and even in the seventies, engines gunked up so bad it was incredible. It was due partially to open crankcase systems but mostly due to the primitive oil that was used. Modern premium oil has the additive packages built in. Adding other additives will badly upset the balance of the additive package that has been so well engineered over the past 20 years or so.
You asked, so I'll tell you. I am an oil change maniac. Oil is cheap, engines are expensive. In my 300E MB that gets only highway miles I change oil and filter every 5,000 miles or six months, whichever comes first. In my Vette that only gets driven occasionally, I change oil and filter every 2,500 miles or six months whichever comes first.
As I described, I use Universal Grade oil, specifically Chevron Delo 400 Multigrade. I use this in everything on my place from Diesel tractors, to diesel cars and gas cars. The only other oil I use is Mobil One in my '01 MB C240. It came from the factory with Mobil One so I have stuck with it.
Additionally, I drain my oil when the engine is hot and let it drain overnight. This is how you get all the gunk out. The gunk is stirred up in the oil when it is hot, so it will drain out. Draining overnight gets the last few drops which are the real sludge anyway.
You already pay for additives when you buy your favorite premium motor oil. There's absolutely no reason to incur the added expense of additional additives. Most of them are snake oil anyway.
If you will change oil every 500 miles and drain it when hot, you will get your engine cleaned out safely in just a few oil changes.
My $0.02,