Pontiac 2 1/16 Steel Cam Plug, Each

Seals the back of the camshaft tunnel on the rear face of the block.

This plug is holding oil, not coolant, and it is the one most often blamed for a rear main seal leak that is not a rear main seal leak. The cam tunnel is pressurized, so a cam plug that is cocked, loose, or installed without sealer drips down the back of the block and onto the bellhousing exactly the way a bad rear seal does.

Like the rear coolant plugs, it is buried behind the flexplate once the engine is assembled — do it on the stand.