The valve cover gasket will leak at the back of the cylinder head, not the block.
The previous owner of our 300TE went spare with an oil leak at the rear of the valve cover gasket that wasn't fixed by the garage even with liquid sealant applied and two new gaskets. I fitted a new gasket and it was instantly leak tight. I did find two issues though. The gasket works best if fitted to the valve cover by starting at the rear end 'loop' and making sure it is square, as there was a small notch in ours with a matching bobble on the gasket. The other issue was that the gasket had a tendency to roll over slightly at the back and it was easy to catch on the valve gear when refitting the cover. It is still leak tight two years on. It needs to fit onto clean metal on the cylinder head too.