I once used Marvel Mystery oil in an '83 Bronco I had because the engine
knocked so bad. Bad idea, it cleaned all the gunk up so good that it ate
away at the rear seal. From that point on the oil pressure in that thing was
always low and it blew oil out of said rear seal. My father-in-law (whose a
mechanic) said he would never use that stuff in an engine as it will strip
away any layer of lubricating sludge that sometimes is good to the engine.
The good thing is that I traded in that truck for my first Vanagon (Vanagon
content).
Peace out,
Peder
'84 Westy