I've had similar results from Rislone. My understanding is that Rislone is an oil plus a strong penetrating detergent or something like that which allows the penetration and softening of the deposits causing rings to stick. Anyway it works well but slowly, which is good since you don't want to release lots of gunk to plug the oil passages.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog