My son recently bought a 97 Monte Z-34. One of the things it needed was to have the lower intake manifold gaskets replaced, which I did. A few months later, what was a minor oil leak turned into a deluge.
This weekend, I fixed it, and thought I'd pass on what seems to have been an effective cure for what I'm sure someone else may be having difficulty with.
After getting the upper and lower intake plenum removed, I removed the crankcase breather plate (approx 2-1/2" x 10") that sits on top of what I would call the cam chamber, if this engine had an internal camshaft. The gasket was brittle and an obvious cause of the problem. However, getting just a replacement gasket was impossible - all the places I checked required the purchase of the cylinder head gasket set - some $333. Instead, I made a new gasket out of standard gasket material and sealed it with RTV.
The oil pump shaft was also a suspected cause of the oil leakage, but removal without also removing the rear cylinder head is impossible. So I loosened it and was able to raise it about 1/8", enough to clean it thoroughly with brake cleaner, and then packed the resulting "groove" with RTV. After letting it set for an hour, I pushed it back into the block and bolted it down, then reassembled the lower and upper intake plenums.
So far so good!