Plutarch, in his Reply (at 1116c) says this -- and then ends with a helpful quote from Colotes:
But I should like to ask the very man (Epicurus), who brings this indictment, if his school does not see this distinction in their own system, whereby some objects are enduring and unchanging in their being, just as atoms too in their doctrine are forever the same because they are too hard to be affected, while all aggregates of atoms are subject to flux and change and come into being and pass out of it, as innumerable films leave them in a constant stream, and innumerable good others, it is inferred, flow in from the surroundings and replenish the mass -- which is varied by this interchange and altered in its composition, since in fact even the atoms in the interior of the aggregate can never cease moving or vibrating against one another, as the Epicureans say themselves.
"It is true" you (Colotes) say "that this sort of difference in ways of being is found in the actual world. But Epicurus shows himself a better philosopher than Plato in applying 'being' to all alike -- to the intangible void and resistant body and to the elements and their aggregates, holding that a common and single way of being is found in both the eternal and the generated, both the indestructible and the destructible, both the unaffected and enduring and changeless realities that can never be expelled from their being and those whose being lies in the fact that they are acted upon and changed and which never for an instant remain as they were."