I think that you now have the car on a good oil change schedule given the oil that you are using. I expect that the previous owner was not so dilligent.

Using the MM will really do nothing for you. A few oil changes of the Mobil One will do as much cleaning as can be done. If you still have the ticking, you might do a quick change or two with a super high detergent oil such as Delo 400. This is designed especially for diesels so it has very high detergent content to accomplish soot dispersal. It is also certified with the latest gas engine rating.

Since it is much less expensive than your normal brew, you can drain the engine while hot to get as much crud out as possible, put in a new filter and a fill of the Delo. Run it about 500 miles and change again while piping hot. This will get out the most gunk. Then go back to your synthetic brew with a clean filter.

This is the best and safest way to deal with a gunked engine. Using non lubricating solvents to clean an engine is risky.

Best of luck,