White powdery corrosion on OUTSIDE of spark plug - cause of misfire 99 Elentra

My son's 99 Elantra's engine was misfiring. Code said #4 was the culpret.
Went to replace the plugs and plug wires (we'd had it over a year - short
trips to/from school - so the non-Hyundai plug wires the PO had on it were
due....). #s 1 - 3 looked normal... no problem... took the plug wire off
#4 and the inside of the metal tube leading down to the plug had white,
scaley corrosion in it. The car had been sitting for a week because I had
not had time to mess with it. Anyway, to me that says that there is some
sort of water or something getting in there. Took out the plug and the
exposed portion of it (metal and part of the insulator) had the same white
stuff on it. Any thoughts? It has run great. No problems. oil looked
normal... no water in it or anything.

NOW, ONE THING.... for the first year we had it, until the beginning of this
year, the car had only been driven in short hops (to/from his school 1.5
miles away). Starting earlier this year the car started getting out on the
highway for about 1/2 hr to/from a different destination and I noticed that
the oil quit getting that sludgy deposit on the filler cap that often comes
when the engine doesn't get hot enough to vaporize the water and other stuff
that gets in it (condensation, etc)... but that has not been the case for
the past 6 or 7 months....

Any thoughts? Sound familiar? I don't see oil in the radiator fluid
either...
TIA
KWW

 

The corrosion in the plug hole probably indicates someone got water in
there. Some aftermarket wires don't even seal the hole. But, if the
moisture's gone, don't sweat the corrosion.

If you're getting the condensation intermix on the oil cap, but nowhere
else, just make sure you change your oil frequently.