Despite what has been stated, WD-40 (Water Dispersement) is excellent for spraying on tools to prevent rusting. The added advantage being that is easier to remove than an oil based product.
I still do oil changes on all 4 of my vehicles. But using old sump oil is just so dirty. Especially from diesel's.a tad expensive for just spraying on tools ..
my dad used to dip his tools in a basin of old engine sump oil ..
remember the days when we did our own oil changes..