I am stumped with this problem - wrote about it originally probably over a year ago. There is an odor noticeable outside of the car especially when parked in the garage only when the tank is filled to the top. I removed the carpeted sections and the metal plates covering the fuel pumps - I don't smell the odor there, but I should check again since when I did this the tank was not completely full. I tried disassembling the plastic sheathing that runs around the gas tank filler tube and all of the hoses that are packed in there - I was able to get one side off but that did not reveal anything. That stuff is so tightly packed and that sheathing is difficult to remove. I removed the large plastic trim in the trunk that runs along the front of the trunk (portion closest to the bumper). There is a vent line that apparently runs through there - don't smell anything. The gas odor seems strongest when lying under the car and sniffing about the center of the bumper - this doesn't make any sense. There are 3 small lines coming from the bundle of the filler tube that seem to go somewhere above the top of the gas tank. One of them is farely solid, one line has a small maybe 1-2 inch rubber hose and connects to another line and has some movement in it, but I can't see where it goes. I am not sure about the third line. Where these three hoses go there appears to be some type of metal plate but it is hard to see. There is also some discoloration of the undercoating around this area. While I do smell gas hear I don't feel any wetness around the discolored area and I don't see any signs of seepage where the filler tube joins the gas tank. I am very baffled by this problem. As I mentioned before the gas order appears to be strongest under the center of the rear bumper -- makes no sense. This is a last ditch effort before bringing it in to have someone with more experience than I take a look. I'm open to any help or suggestions.

And just to be clear the car has what I believe to be an 18.5 gallon tank. If I fill to 16 gallons I don't seem to have any gas odor issues.

 

I would pull the covers again and check with it full.
Either a hose is bad or the sealer around the pump wires is gone and it is leaking through there.

 

Looks like the sealer around the pump wires is gone. Although gas is not visible on the top plastic part of the pump assembly it is kind of dirty so there may have been a few drops of gas that attracted some debris. There is a strong gas odor when the metal cover is removed. Looking at a diagram of the pump assembly, I don't understand why it would be any different when the tank is full or not. Not having actually looked at a real fuel pump assembly I'm guessing the top plastic part is somewhere in the neighborhood of 6-8 inches from the fuel pump, so whether the tank is full or not I would expect to have the same problem? Maybe I'm missing something obvious? Problem only happens when the tank is full and surprisingly not right away, it may take a few days to show up, assuming I let the car sit with a full tank.

In a situation like this given that the car has 125K miles, what is the best alternative. Cheapest fuel pump assembly I could find by Bosch is in the neighborhood of $300. I could try and clean the area where the wires exit and seal with epoxy. That area will be difficult to clean so don't know how good a seal I will get.

I didn't see any cracks in the top plastic part of the assembly, except there appeared to be a small plastic projection near one of the wires (maybe 1/8 inch tall) that looks like it broke off.

So epoxy, some other sealer, replace the fuel pump assembly, or ??

 

If it were me I would replace the pump and be done with it.

 

Good call, finally bit the bullet and replaced the pump. Problem seems to be fixed now, thx