I currently have a 383 (stock cam and compression) with an Offy intake and Holley 1850. Intake is sealed well with Felpro valley pan and RTV on both sides of the gasket around the ports. The carb studs had to be 3/8" dia, as that is what the intake required, so I drilled the carb bolt holes to accept this. Carb is sealed well to intake. PCV system and breather was working well and their is no issue with that. The one thing I didnt do was add thread sealer to the intake bolt threads, but I doubt that has any effect.

The car runs great, has excellent torque and idles smoothly. The odd minor issue that I am noticing is that there is a bit oil staining to the rear and left sides of the intake just under the carb base, after running the car for a while. I will wipe the intake off, then drive again to work the next day (50 miles), come home, and a bit of staining will be present again.

With all of the above taken into consideration, what could be the cause of oil being pulled up through the carb base gasket? There is a small amount of oil smoke out the exhaust during a hot start after sitting a bit, but that may be attributed to slightly worn valve seals.

There are 60,000 miles on the motor. Excellent oil pressure.

I have seen oil leak at the intake bolts before. Ron

With my luck, John is right.

COULD BE a blow-by problem ...

Possibly, but if so, very minor. There is very minor oil seepage out of the left valve cover breather, trailing down onto the valve cover rail after a week or so, but not major. Doesnt really show signs of a major ring issue, as it does not smoke on acceleration on cold start up. A few plugs had a small amount of oil after a 1000 miles, but not fouled by any means.

I have a Pertronix Ignitor I setup and FlameThrower coil, but still hooked to ballast. I need to bypass the ballast to get 12v's to the coil, which may help keep the plugs cleaner.

Should not be any oil on the plugs AT ALL. I would do a compression check or BETTER YET ...a leak-down-check.

Should also clarify that only the valley pan/gasket was used, not individual side gaskets. A criss cross torque pattern from center out was used.

Also, I have been experimenting with the ventilation system, to see if it is functioning correctly. With a PCV hooked up and breather on the other valve cover (both in good order and hooked up properly), I did notice more oil streaking down the side of the manifold under the carb base. Currently, I have breathers on both valve covers sans a pcv and there is a bit less oil. The PCV must of been throwing more oil at the carb thru vacuum.