Since I have been doing my own oil changes in my cars for over 20 years, my well trained mechanic told me to add 1/2 pint of ATF to my oil changes in both my diesel (230K)and gasser (120k).

This is in my mind and will not leave until I can understand it. Has anybody heard of this before. Is it somthing done with the old not so good oils of the old days? May be to keep the top end lubed?