long-standing 300E(1986) gas smell

Has anyone else with a 1986 300E gas model (automatic), experienced this problem?:
I have owned this MB since 1989. Currently has about 70,000 miles. Often, after cruising on the freeway at the usual legal speeds, when i exit on the off ramp and come to a stop at a traffic light, I will smell gas fumes in the car. MB has been "adjusting" something for years when this occurred but the problem recurs. Something to do with a fuel shut-off valve or regulator valve. The car runs and drives great with excellent fuel economy. Does anyone have a fix for this long-time annoying problem? Thanks in advance.

Al
Vancouver Island