i just had a look around the engine bay of my mates r32 with an rb25 and found i got a broken exhaust manifold stud at the end of the manifold side, and underneath it, on the block there is a patch of oil and it is only under the side of the broken stud, nowhere else, is this oil the result of the broken stud or from some other cause, now the car doesn't leak any oil on the ground, oil pressure is good, and he never has to top up oil or anything, its always on a good level, is this a worry???, thanks