My 1992 Caprice Station Wagon with L05 5.7 TBI V8 engine had been suffering from major blowby, to the point where my low oil level light was routinely coming on, even after top-offs, and I had to replace my PCV system with breathers. The breathers would then become routinely saturated with oil, and it became the norm to smell either crankcase stink, oil burning on the exhaust manifolds, or both at the same time. Oil level continued to be problem. At idle, a visble jet of blowby smoke emitted from both valve cover breathers.
On a whim, I decided to top off the system with MMO, instead of oil out of the 2 jugs of Rotella T5 I came to carry in my wagon. The first "benefit" I noticed was that the crankcase stink was replaced by the not-all-that-bad aroma of MMO.
After about 800 miles, fuel economy and power made a definite jump. Doing 95-100 on the highway no longer required alot of throttle pressure, and highway driving, even with the huge R4 AC compressor going no longer resulted in visual declines of the fuel needle. I started with about 11-12mpg highway when I bought her, and between the Seafoaming and MMO, she got up to 17mpg on the highway, the major emissions from the valve covers has ceased, and my daily check of the dipstick reveals the oil no longer goes anywhere but inside of the engine. After I tested the new AC Delco wires that came with the car at 9K ohms or greater, I replaced the wires with stainless steel marine wires (.9-1.1K ohms), and replaced the Delco platinum plugs with NGK double platinum V-Powers, netting a new highway fuel economy of 20mpg @ 90mph.
At 90, she'll sometimes get away from me and creep to 95 if I'm not paying attention, and will crack 100 easily with very little persuasion.
Once I have redone all of her old seals, I plan to switch to a full synthetic. T6 is out of the question, because of the 40-weight. I want to stick with 10/30. I have no catalyst, so I can run any motor oil I want.
Long story, short: The **** works. 
I don't know exactly what it does or does not do, but I do know that I was about 5 minutes away from pulling the engine until the MMO. She still might get that treatment anyway, just because I want a fresh, more powerful build before I drive her down through South America, but in the mean time, at least I don't have to put up with any more of the oil drama. 
