Oil leak at top rear of engine

 "74 350 with Edelbrock performer intake.  I bought the car with this engine/manifold and it always had small drops at rear of engine.  Recently distributor to HEI with tach drive.  Started engine, no problems.  Took car for drive and smelled burning oil.  Looked at engine, found puddle on rear below the distributor on the driver side.  Pulled distributor, made sure gasket was there and not broken (put on new one with distributor).  Wiped up oil and sprayed with brake cleaner-all bright and clean.  Started engine, let it idle a good 5 minutes-no oil.  Took her for a drive around the block, and it's got a puddle on the back of the block again.  Any ideas where this is coming from, and how to fix it?

Rear valley of the intake manifold would be my guess.

YUP! My guess also. If they used the O.E.M. style rubber gasket and not RTV, it probably slid out of position when the manifold was installed. They get real slippery when put on wet. Dry is not so bad, but still need to be extra careful when lowering the manifold into position. Gonna need to pull it to do a good job.

Valve cover gaskets or oil pressure gauge fitting. But intake rear gasket most likely.

After consulting with my local Hi-performance Chevy mechanic and race car builder, I removed the intake manifold.  Found the rubber gasket at the rear was glued in with a little red silicone, which was where the leak was (the silicone had blown out, the gasket was still in place).  cleaned off all surfaces, replaced gaskets on the heads )glued them down with Permatex "The Right Stuff" which was recommended by the mechanic, and built up about 1/4 inch of The Right Stuff at the front and rear of the block.  Torqued manifold back down, no more leaks!  Thanks for all the suggestions, it turned out to be what I had suspected all along.  By the way, the oil pressure sender is on the side of the block, there is a plug in the rear.

GREAT! Have replaced many of them the same way. BTW, the sender on the side of the block near the filter is ELECTRIC. The one on top of the block near the distributor is for the pressure line for the gauge in the cluster in the center. It is a wet line from the oil gally. It shows REAL pressure. Not electric.

If the previous owner installed the intake with the rubber seals at the front and rear of the block and also used RTV sealer, that would cause a leak, you want to use either or, but not both. HTH, Ben Smith