Would it be possible to use the base oil group as a rough guide to time of use? For example group 1 use for 2-3 months max, group 2 use for 6 months max, group 3 use for 1 yr. max, group 4/5 possible useage 1yr.+ up to about 2-3 yrs. max. Yes add pack is important, as is the total product, but adds generally compensate for the bad things of the base oil so even they vary with the base oil.