rr, when you change filters at whatever interval Blackstone tells you to do, you always add or top off after replacing the filters which is usually aroung a half gallon of oil so you keep replacing the additives you mention. It works for big rigs and machinery so it works for us also.
Bud

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1987 300D Turbo, 175k mi., 1998 BMW 323i Convertible, 1997 F250 4x4 7.3L PSD