I would guess if a car has an oiler system that is what it is meant to have, i am sure i have read somewhere that the kingpins on oiler cars where not designed to be greased from the top. On the basis that modern oils are thinner, I have fitted lathe oiler cups to gravity feed clean oil instead of squirting an unknown quantity of used oil from from the engine. Not very technical as it requires personal judgement, but little and often seems to keep the pins oiled without it washing out the grease or dripping out, works for me but may not suit everybody.
As for grease nipples i would order two of each as they are cheap, the ones you have over will make a nice pair of earrings for the other half.
