Rejuvenation and/or extension of the lifetime of frictional performance in transmission fluids

A rejuvenated, used lubricating oil composition comprising an admixture of:

• a major amount of a fully formulated lubricating oil composition that has been previously used to lubricate a vehicle transmission for at least 25,000 kilometers, or a lubrication running time equivalent thereto, the fully formulated lubricating oil composition having comprised, prior to use, at least an anti-wear additive, an ashless dispersant, an overbased calcium detergent, a friction modifier, a corrosion inhibitor, at least two additional antioxidants, and a lubricating oil basestock;
• and
• a minor amount of a suspension-stable transmission fluid booster additive package composition that maintains suspension stability when added to the previously used formulated lubricating oil composition, which booster additive package composition comprises:
• (a) anti-wear compounds consisting essentially of a mixture comprising:
• (i) two or more compounds of structures (I):
• where groups R1, R2 and R3 are independently alkyl groups having 1 to 18 carbon atoms or alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage, provided that, in component (i), at least one incarnation represented by at least one moiety from the mixture comprising structure (I) as functionalized in a set of all groups R1, R2 and R3 in all structure (I) compounds, collectively, are alkyl groups having 1 to 18 carbon atoms where the alkyl chain is interrupted by a thioether linkage;
• and
• (ii) one or more compounds of structures (II):
• R4—S—R5—O—R7
• R4—S—R5—O—R6—S—R7 (II)
• where groups R4 and R7 are independently alkyl groups having 1 to 12 carbon atoms and R5 and R6 are independently alkyl linkages having 2 to 12 carbon atoms;
• (b) an ashless dispersant;
• (c) an overbased calcium phenate detergent;
• (d) at least two friction modifiers, a first of which comprises a polyethylene polyamine succinimide derivative, and a second friction modifier comprises an amide friction modifier, an amine friction modifier, or a mixture or combination thereof;
• (e) a corrosion inhibitor;
• and
• (f) a suspension-stabilizing amount of a lubricating oil basestock, wherein the rejuvenated, used lubricating oil composition exhibits:
• a boron content from 30 to 400 parts per million by mass, based on the total mass of the rejuvenated, used lubricating oil composition;
• a calcium content from 250 to 800 parts per million by mass, based on the total mass of the rejuvenated, used lubricating oil composition;
• and
• a phosphorus content from 250 to 800 parts per million by mass, based on the total mass of the rejuvenated, used lubricating oil composition.