Over the past few days, I have noticed a strong odor of gas fumes in the cabin of my '92 400e (71K). The odor is also present when opening the trunk. There are no visible fuel leaks from anywhere underneath the car. I did peel back the carpet, etc. inside the trunk to examine the fuel filler neck and fuel tank and did not notice anything unusual or any apparent fuel leaks. Could this odor be coming from a worn/faulty fuel cap gasket? If not, what could be the problem? How do I fix it? Thank you in advance for your assistance.