I had a customer that insisted on running Amsoil. She would not change oil, only the filter, as Amsoil recommends.
The restrictor on her engine was always plugging up to the point I drilled the restrictor oversize so it would not.
If you don't find the fitting plugged(which you will) try running the engine with the fitting out to see if oil comes out of the hole.
If no oil there then the cam bearing is in wrong, or in very bad condition.
