I have a large amount of oil (brown sludge.

Hi, I have a large amount of oil (brown sludge) in my antifreeze reservoir and cooling system, and there was bubbling/pulsing in the reservoirlast time I had it running, but there is no apparrent coolant in the oil. I drained the oil and it all was black and good looking, no milkshake. I started taking things apart, and when I pulled the thermostat out the intake manifold gasket is visibly blown out, looking in the hole where the thermostat goes. Is it possible that this hole in the intake manifold gasket can cause my condition of oil in antifreeze but no antifreeze in oil? If so it would make this a lot cheaper and easier fix than if it something more serious like a head gasket or cracked/warped head. Is it worth just trying to replace the intake manifold gasket first or does it have to be something else more serious to cause the condition I have? I am working on this in my driveway with minimal tools and very little knowledge of mechanics, so any help would be appreciated! Thank you