I have a 78 L-82 with aluminum valve covers, and the passenger side one persistantly leaks at the gasket on the lower rear corner. I have had the head magnafluxed and found no cracks. I have purchased a new valve cover incase the old one was cracked. I have tried every gasket that I can find - standard cork, extra thick cork, metal core, rubber based. I have tried each of these with and without sealants and still the leak shows again after a few hundred miles. Does anyone have the same problem? Misery loves company. Does anyone have a suggestion on how to stop the leak? Help!!!

This is a long shot, but check your PCV valve and tube. If it's clogged, excessive pressure can build up and cause the leak. Like anything else, the pressure will find the path of least resistance to vent, and maybe that area of the valve cover and gasket is the weakest.

I know this is too obvious, but it actually happened with my ride: Check for irregularities on the head ridge where the gasket makes contact. A tiny wart in the casting will give you a dribbler. (Mine dribbled onto the oil pressure sender, making me believe I had a leaky sender!) Find wart, grind off.

Two of the best gaskets that I have every used.

One - Earls Pressure Master Seals.

Two - ROL Hyper Blue- This gasket actually swells when in contact with Oil to prevent Leaks.

I have never had a failure with with any of these gaskets.

Also, torque the valve cover bolts to equal specs. Over torque and you could warp the Valve Covers or distort the gasket where it won't seal. The earls pieces prevent this problem.

Find a valve cover that fits your engine and install it with a new gasket. That will tell you where to look for the problem. If that solves your leak, you know that the valve cover has a bad place. If not, you might have a problem with the ridge on the head.
Tom