[V8] snake oil?

[Kent McLean]

Let's say I haven engine with a lot of miles on it. Let's say
I can see brown stain, for lack of a better term, on the internal
bits when I take off the oil cap.  Let's say I'd like to clean
the insides of the engine.

What would you use? Some of the "cures" I've heard include:

Rislone Engine Treatment
Marvel Mystery Oil (MM)
Automatic Transmission Fluid (ATF)
synthetic oil as usual

Others?

Or are they a waste of time, money, and effort,or do more
harm than good?

Thanks.

-- 
Kent McLean
'99 A4 Avant, V6 Tiptronic
'91 200 TQA #3, with mods
gone: '91 200 TQA x2, '94 100 S Avant, '89 200 TQ