Now theres a good &^%*ing idea.
Agreed, I used too run MMO,Seafoam, B12, snake oil and Stay-Togeather-Please in all my trucks. Now I settle for a engine flush every 30k using Gunk. Buts thats a idle for 10 minutes and then change other wise it may kill your botton end stuff.
MMO works, but all it does is clean your engine/injectors/valves depending on were you use it. I mean its a solvent, people use it too free stuck rings and to remove cylinder wall glaze. Do you really want a solvent in your oil?
STP and Lucas are heavy weight oils with additives that do the same thing. If I were to run anything for the duration of a change it would by STP or lucas, since it doesnt thin the oil out. For cleaning the fuel system it would be one of the solvent based fluids (MMO,B12, Seafoam)
But thats just me, I'm not holding your head under water demanding that you believe in the all mighty god STP (or MMO,b-12, etc.)