Had the same issue with one of my plugs today. I did a complete tune-up (sparks, wires, throttle body clean-up, new PVC valve, MAF sensor clean-up, EFI sensor re-set, k&n filter re-charge, and oil change).
BTW, I didn't know jack sqwatt about 98% of the aforementioned work until I read this forum for about three hours last night. Great stuff.
I'm gonna call around about VCG replacements this week. That may be out of my comfort zone. Then again, if the cost is too great, it might be back in my comfort zone...
I'm pretty sure it's the VCG because it's just the boot end of the plug that's oil-covered. The rest is pretty clean. There's quite a bit of oil coming out from under the valve covers, too.
Will advise.