Ok, lets go back to basics here....
A FUEL smell is caused by only one thing, a leak of oil.....
If you can't find any leak evidence the only other place to try would be in the blast tube, when firing you could have a small drip from the nozzel fitting (this can also present and a small whisp of smoke that travels back and out arount the mounting flange when firing......
Other than that, if there is no evidense of oil leaks at the burner, pump (check all pipe connections and blanks) or on the hydraulic jack (none on the G5x) at the fire valve, flexible hose, filter bowl, all connection at both the last two listed, remember it could be a very very small leak you can still smell, and lastly where the plastic sheath ends on the copper pipe comming from the tank (if you find it there, the actual leak is usually at the tank, and is travelling the whole pipe length between the plastic and a copper inner to come out there)
Failing all that, a line pressure test maybe required to test your line right back to the tank.
The other is fume or boiler smell.....a completely different set of issues that often get mixed up
this can be caused by improper setup of your burner air/fuel mix (have a FGA done by your serviceman) or couldd be down to poor or degraded seals on the boiler or burner mounting flange, a leak at the nozzel as discussed above, flue gas recycling, bad flue joining or seal at the boiler or along its length. Thats about all I can think of at first glance...
Hope that is of some help...