like many on here, i had the same missfire / spark breakdown.
i used the silicone method. covered them in selleys 401.
i also clean the spark contact inside till it was shiny and gold.
both these things helped alot, but there was still an occasional weak spark in cold weather at 12psi.
another member suggested the contact springs.
so i pulled the coils out again, and this time i stretched the spring that contacts with the spark plug, about 10mm or so. (i'm not sure if the S2 R33 and R34 use a spring, but the S1 definately do).
so now the spring pushes hard against the spark plug, and reduces the chance of poor contact/stray spark.
that was a few months ago, and no problem through the rest of winter and so far. but i'll know for sure once the winter temps drop low again.
just another thing to try