This is what you need to know, article by Rick Lake
Before ripping the motor apart how about we do a couple of easy tests. Coolant pressure test to see if the system is holding. If not, looking at intake gasket and not having to pull heads off motor. Compression test and a leak down test will tell us alot about what is happened to the motor. I would also go with intake gaskets. Is there a milk shake look of the
oil to start. Is the dipstick reading over filled with
oil?
Oil cap have a light brown or water on it? Just pull the valve covers and lets see what we have first. If there is some brown looking cream on the valve covers we have a coolant oil interaction. Might be just the intake gaskets or could be the head gaskets. This is the reason for compression and leak down tests. You want to compression number to be within 5-7% of low to high numbers. Leak down test you want to have about the same of 5-8% in all cylinders. If these numbers come out good, it's not likely to be a gasket for the head. Also at this point check all head bolts or studs for good torque reading. If everything checks out to this point, pull the intake. You said you are on the 2nd or 3rd intake gasket?? If so we need to look at the angles where the heads meet the manifold and where the bottom of the intake meets the block and check the angles. If anything was machined pass .005-.010" the angles could be too far off for proper sealing of this gasket after enough heat cycles. The other thing is how you install the gasket and what extra things are you doing. Heres a short list of what I do and have gotten 7 and now 8 years out of Fel-pro gaskets
Clean both surfaces, you know this. Check the angles with the intake dry on the heads and block do a light bolt down with 5-10 pound of torque on the bolts or nuts. Get a feeler gauge and you want less that .003-.005" to slide between the mating surfaces. This is for intake to heads only. If this is in spec, install gauges. If number is higher, how much? If you have over .010" This could be a sealing problem. If numbers are in spec, Get gaskets and spray 2 lite coats of Hi-TAC on both side of gaskets and let dry. Add a thin coat of GREY sealer to both top and bottom of gaskets and give it 3 minutes to skin. At this time put a nice bead on the motor block where the intake is going to rest. Install the intake gasket and make sure it's centered on all the ports and bolt holes. I know you are strong but need a 2nd person to install intake manifold to get an even drop down. Make sure the gasket don't slide down. Some guys use studs on one side of the motor to prevent this. Torque bolts or nuts in pattern from center out in 5-10ft pound incroments untill reach 30-35 torque reading. This sealer needs 24 hours before added fluids or running motor. This step is over looked many times and this can cause gasket failures. I use a Felpro 1247 gasket and got 7 years out of it and then rebuilt my motor to a 482 stroker that now has 8 years on it. The block, heads, and intake are all aluminum. The expansion rate is the same but more that an iron block, heads, and intake. Good luck, hoping it's the intake. Rick L.