I have had the scrap metal from the Duster X model for ages and was getting tired of checking on the Duster V spawn. So I started killing Scrubber IV models which are placeholders that don't despawn like they are supposed to. They conned indifferent and light blue to me at 18, easy to kill and gave a small amount of experience. They did not alert or cause any other mobs in the zone to aggro, nor did they give a faction hit or loot. After killing 3 of them about 10 minutes later the Duster V spawned, killed it and got the other scrap metal for the Bootstrutter Framed Backpack turn-in.
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I have heard people saying not to kill the Scrubber models because they give an Akanon faction hit or they cause other clockworks to aggro. I think they may be referring to Clockwork Scrubbers. Different mob altogether.