I used gunk brand engine flush. it's similar to kerosene which could also be used. some even use transmission fluid. I used 2 quarts because we have much more than 5 quarts capacity. the instructions say to just run at idle for 10 minutes & dump the oil, I ran for 15 minutes & also rev'd it slightly to 2,500-3,000 rpm to help break down deposits.
after dumping the oil from the flush I filled with inexpensive oil & a double sea foam treatment and another aditive that claims to free up stucky lifters & rings.... run that for 1,500 miles or so then dump & fill with 7 quarts of the good stuff & one quart of lucas synthetic additive.
before this treatment my S500 came to me clacking like a diesel. it was so bad that some of the lifters were just collapsed and I had steady misfires on 3 cylinders. it barely ran and it ran like crap. I was at the point of deciding weather I wanted to buy all new rocker arms & do the huge job of replacing them or just buy a junk yard engine because it just seemed like the motor was really screwed up, but then I decided to try flushing first...
after this flush treatment then the aditive cycle and some time, my S500 now runs like a baby... the engine is now dead silent & runs like brand new, really runs strong... the clacking at startup got less & less until it just went away completely
now I'll run a lucas with every oil change of mobil 1 0w40 for ~5k miles each & then every third or forth one will get another seafoam treatment.
I'm also a big believer in sea foam in the fuel system. I'll run a highly concentrated mix through a low tank once in a while & blast it with some full throttle runs, really cleans up the injectors valves and combustion chambers of carbon deposits and also helps eliminate carbon deposits from forming, mine was a little rough until a few good fuel system clean outs too, cleans the fuel injectors nicely