Jay,

I rebuilt my 350 about 30 years ago. I'm taking it apart this month after 25k miles. I had oil leaks as the pan was wet and also the transmission. After looking it over I found the leaks. The rear and front crankshaft seals were leaking. The pan gasket and the timing chain housing held.

Also, no antifreeze leaks what so ever.

This is what did:

Water & oil part connections: gaskets + blue Form-a-gasket on both sides of the gasket. When I assembled it I just snugged up the bolts and wait for the silicon to almost setup, then I tighten them with proper torque.

Heads: Spread a thin layer of GM Lubriplate 105 Lubricant (white GM grease) on both sides of the head gasket. My dad taught me this trick and so far no blown head gaskets. The grease eliminates any binding of the head gasket when you torque the heads.

Also, torque and the order you torque the bolts are very important. Get a general book on engine maint or rebuilding for Pontiacs as a guide.