Oil on ONE spark plug, some engine issues Options

[RoadRage]

Hey guys,
Currently I have an oil leak that is pretty bad, and its suspected from the oil pump seal, I have ordered a timing belt kit and all the seals for a replacement job, but today while driving home I noticed when stopped at a red light the car with fluctuate up and down about 50rpm (from its normal 900, to about 850)

I get home and let it idle in the driveway and it doesn't do it anymore..
I take a look in the engine bay and see my pod filter is pretty dusty, So i thought that could be the cause, but I took a look at my spark plugs and one of them is very oily (it's the one closest to the timing belt)..

It was last serviced at the start of Jan and it got new spark plugs, about 2 weeks ago when the leak started, I had the gasket cover replaced thinking thats the issue, however the car still leaked)..

I started the car again thinking the 50rpm thing is me going crazy and after starting it and it gets up to normal temperature. It fluctuated about 7-8 times until it stopped and stayed at 900.. after keeping an eye on it for about 2 mins and still at 900 I turned the car off.

I'm not the best about these things and I am trying to learn new things everyday so would anyone know, is the oily spark plug the cause of these fluctuations and how come it only does it a few times then stops?
Is it possibly related with my current oil leak and if I get new plugs (I definitely am) will it stop the leak, or do i need a new cover again?
Or something else I'm not aware of

Thanks

This post has been edited by RoadRage: Apr 1, 2014 - 9:04 AM