I'm not an expert and believe me there are some real knowledgeable people on this forum.

A couple of ideas


Depending on your piston rings a minor amount of gas will get into the oil pan. That is part of the reason for changing oil every 3-5K, longer for synthetic.

Nothing like you mention about your issue is normal.

Question

Had you done some previous repairs. You stated that the car was running fine then the gas problem then you changed hoses and oil ran fine for some time then the same problem

Why did you change hoses on the back of engine?

Possible items:

1. Stuck open fuel injector (not familiar with the 450 system but my 560 has injectors)

2. High pressure (Fuel pump) in the gas line pushing gas past the piston rings

3. Head gasket going bad. Did the car run poorly after you changed hoses and changed oil?

That's a couple of things

Hope this helps to get you started