Oil on top (connector) end of spark plugs ?!?

["Chris Newbold" <cnewbold@earthlink.net>]

Today I was installing a new set of plug wires (from Blau) when
I noticed something very odd. Two or three of the plugs seemed
to have engine oil on the connector and the very top of the
porcelain. There was no evidence of oil in the well surrounding
the plugs nor on the inside of the connector on the end of the
wire.

I installed these plugs myself about 18 months ago, so I know
there was no oil on them at that time.

Any ideas how it may have gotten there? I don't really like the
looks of it, though...

-Chris
1993 90CS 5spd 75k miles