Plug wire (carbon fiber) should have the 10,000 ohm resistance per foot standard. (Mag wire is a whole lot less). As these are 6 inches, so 5K max is the fail point. Personally I would just replace them as they are cheap. Add a dab of Die Electric gel.

Info source:https://en.wikipedia.org/wiki/Silicone_grease
Dielectric grease
Dielectric grease is electrically insulating and does not break down when high voltage is applied. It is often applied to electrical connectors, particularly those containing rubber gaskets, as a means of lubricating and sealing rubber portions of the connector without arcing.
A common use of dielectric grease is in high-voltage connections associated with gasoline engine spark plugs. The grease is applied to the rubber boot of the plug wire. This helps the rubber boot slide onto the ceramic insulator of the plug. The grease also acts to seal the rubber boot, while at the same time preventing the rubber from becoming stuck to the ceramic. Generally spark plugs are located in areas of high temperature, and the grease is formulated to withstand the temperature range expected. It can be applied to the actual contact as well, because the contact pressure is sufficient to penetrate the grease. Doing so on such high pressure contact surfaces between different metals has the advantage of sealing the contact area against electrolytes that might cause rapid galvanic corrosion.

Yes. I know this is not a College like MIT test posting, but it is good enough for a DIY site. This is to save myself from a response...

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
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2002 M5 TiSilver
2003 525iT
1998 528i
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1971 Dart Sport, “Dart Light” package
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