where are camshaft plugs located and how many?

The camshaft plugs are located in the cylinder head just under the surface of the valve cover gasket. They are there to fill voids left when machining the surface in the cylinder head that the camshaft rotates on. The cam plugs on older Toyota engines were made of rubber and over time got hard and brittle and did leak. Newer Toyota engines (yours) have these plugs made of aluminum and do not need to be replaced if it thought they are leaking you can take them up, clean both surfaces and use sealer on them. I forget the cut off date for ignition distributors on that engine but the distributor O-Ring is a frequent oil leak area as well.