Sounds like an issue I had 2 years ago. It is difficult to tell where the oil is coming from and certainly I was fooled. I thought it was coming from lower down but in fact I solved the problem by replacing the front rocker cover gasket. A very easy job. Unfortunately, the rear gasket started leaking last year and that is not so easy to replace. It seems these gaskets have a shelf life and at 330,000kms, mine are reaching that life. The front gasket went when I was in Mexico and one of their many remarkable mechanics performed a temp solution with silicone. That cost about $20. The silicone got me home but the smell of gas returned stronger each day. Since I had seen the mechanic do the job, and I had bought a new gasket in the states when I was passing thru, it was an easy fix for me to change the gasket myself.
In conclusion. Before getting into a difficult and costly job dealing with the manifold, try replacing the cover gasket.
Lockie