nachschmieren: Es gibt kaum einen Unterschied zwischen "schmieren" und "nachschmieren",
wobei "nachschmieren" wirklich bedeutet, wieder zu schmieren, während "schmieren" einfach schmieren bedeutet.
lubrication: There is very little difference between "schmieren" and "nachschmieren",
the later really means to lubricate again, whereas the former simply means to lubricate.