Ding ding, We´ve got a winner Jonny. That is more than likely exactly what is happening. Especialy if you have a CVH motor, i.e. 1.9L or 2.0L SPI motor. Since the spark plugs are below the gasket line of the valve cover it´s quite easy for oil to drip down into the spak plug area. If the tips are dry then you are in good shape. Had the tips had oil on them too you most likey would have a leaky valve stem seal, or a piston ring problem. Valve stem seals are some what easy to replace, but pison rings.... ha. So run out and get yourself a new valve cover gasket, and slap that puppy in there. While you have the valve cover off look inside the valve springs, and see if you can see any probs with the valve seals, just for peace of mind.