I have some oil residue on the header bolts, mainly on the 4th and 3rd cylinder. THe car has been runing this header about 4000 miles, very hard most of them. I did a valve adjustment and did not replaced the rubber gasket of the cover, but the car has not run more than 50 miles after it

 

Just to be on the safe side, do a leakdown test

 

As has been already said, a little bit of oil at the front of the chain case will not compromise cylinder pressure.