Actually, 10 ohms is next to nothing and should not affect running at all. Plug caps known as 'suppressor caps' often have upwards of 10,000 ohms resistance; these are the ones to avoid. Your plug caps are probably designed to be zero resistance, 'straight through' types, and there may be some reason to do with their construction, maybe the materials used, why they have a little bit of resistance. As plug caps are only a couple of quid I'd probably get some new ones anyway.