MMO is mostly relatives of kerosene. It will get behind some deposits, not a lot. If the ring lands were a bit gummy, it could have loosened them a bit. But the fact that your motor responded to an additive at all, suggests that it has issues with deposits and/or varnish ...
BG109 or KREEN will not loosen stuff in waterfall amounts, so they don't clog motors. It works on parts that are rubbing or opening and closing like disc valves, etc. W/o the activity, it does not do a lot. A bazzillion folks have used both and never lost an engine. So if you have known deposits, I'd rather get them loosened and away from parts they can effect.
I can't get KREEN shipped into Cali
If I could, it would go in every motor that was new to me. 3,000 miles later I'd do the oil change, and use BG109 out to 5,000 and then at least the next three or four changes ...
As it is, for motors with mileage under their belts, I use a can of BG109 every change. My wife's JAG, the Bronco (218K and counting), and the new to us truck will get it. In a few years, the motor will be spotless. I could do that in a year with KREEN and three changes
Ring lands, hydraulic lifters and variable valve timing are all areas that are adversely affected deposits and varnish. And cleaning each can add to performance and improved mileage. The fuel reduction relieves the engine of fuel dilution getting by the rings which leads to further varnish ...
Regular old every day sludge on valve covers and such does not do much harm. A motor with parts that are free to do what they are supposed to do is the goal. You are part way there. Finish the job somehow and you will be happier with your ride 


