Megulawn

2012 Audi A8l 4.2 V8 - 101K miles

I have a few issues that I need assistance with, see below:

- Oil in spark plug tubs. I am assuming that it is the tub gasket in the head. Is this something that I can accomplish or should it be taken to a shop? Of course this causes the check engine light to come on due to fouling out the plugs.
- Check engine light on some codes state that the mixture is too rich. Would this also have to do with the plugs having old on them?
- Car has a hard time starting when driven over 20 miles, once it has warmed up.
- Once the fuel gauge hits the 1/2 mark the check engine will go out. When more gas is added the check engine light will come on even when not on before.
- Back up camera is out on the screen but all other functions work.

Any guidance would be most apprciated.