Oil Leak?

I have always had an oil leak in my 383, at the rear of both. I have tried everything. Worst was when I had stiff cast aluminum covers and stiff silicone gaskets. It almost poured. I broke the end off one cover trying to tighten it. I found that the gasket surface on the head isn't flat, but angles down ~1/8" at the rear. Also, the casting flash makes it harder for the oil to drain back, so the level gets near the gasket. It is tolerable now, after going back to the factory covers and rubber gaskets, just a slight seepage, though it does gook the starter. If I ever remove the heads again, I will have a flat surface milled for the gasket. The factory cast lip was a poor design. I haven't driven my 273 enough yet to compare. My slant six always leaked a bit, but could have been more from the spark plug tubes.