ADC sold a zillion of these bodies that look almost alike (aside from the colors of the plastic bits and/or the metal body shells), and so many ADC bodies have had random styli (especially the K8s) stuck on them over the years, that before we go any further we should establish which of the three body varieties you have so you can match it with a stylus that will give flat response, or, if we can't get flat, a treble that's not "bright".
How to find out exactly which of the three "flavors" a given random ADC body is? First, we need a good sharp closeup photo of the cartridge, preferably off the tonearm, and second, we need a resistance reading of the cartridge's left and right channels using a digital ohmmeter capable of reading resistances between 250 and 850 ohms.
Once we determine which class your body falls into, we can say which styli will sound best in it. Fortunately, there are still good originals available.
This is an original genuine K8 conical stylus in a K8 body:
Later, production was moved to Japan and those styli look different:
I tried one of these and didn't find it to be built like, or sound like, the originals.
However! At some point in US production, ADC changed from the bright blue to a subdued, somber gray. These sound great, track well at 2.0g and can often be found for bargain prices.
Wualta's implied suspicion that someone had cheaped out on a replacement stylus - the three you have are among the cheapest, least desirable styli available for ADC cartridges - would seem to be true.
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