If your car has a remote
oil filter (especially if it has an
oil cooler) you might want to check that the
oil hose lines have not been reversed. Some oil filters will allow (though not very effeciently) oil to flow backwards through the filter. Most oil filter won't let any oil to flow through them at all if the lines are reversed. It could be possible that they have always been wrong but latter someone changed oil filter brands. May not be the problem but worth an investigation before pulling the motor.