if you take the existing intake off clean the intake gasket surfaces real good. do the same on the cylinder heads. put the intake back on and just put bolts in the corners of the driver side and one bolt in the corner by the distributor on the passenger side. don't torque them down; just enough tension to locate the manifold. then take a .010" feeler gauge and run it along the top side of the intake and bottom side noting anyplace the gauge will slip thru. pay special attention to the #6-#8 area. if you have one of those flashlights with a flexible light to run thru the valley area it's a big help. be patient doing this. also look at the intake just below the #2-#4 ports and #5-#7 ports to see if there's a cast in extension that hangs below the port window. i believe those "extensions" at the gasket surface mess up a good seal with the fel-pro gaskets. i know 6pak intakes and a ch28 intake i'm using has them, also factory iron. i have an old ch4b that doesn't have them and it fits perfectly. anyhow, neither of my 6pak or ch28 have those problem areas anymore. i've used rtv for a gasket sealer before and generally rtv and gas don't get along well, but i have found the ultra gray to be an exception and it's all i'll use now. i also think you have more than an oil leak problem looking at those plugs. after the intake problem is solved i'd do some serious tune-up work.