Car Studdering / Hesitation Engine Light On Puttering While Idle

The wires are NGK recently replaced no more than 5K ago, same with the plugs, when I pulled out some to check, they looked normal, not burnt, and not totally white, but the bottom of it, on threading seemed to have some oil on it. I remember at 30k when pulling out the stock plugs it had a bit of hint of oil on it too, is this normal?
TIA
 

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