Sorry for the late post but I hope it is still useful.

When I first bought it my 1988 560SL had a fuel odor until startup and driveaway. There also was no evidence of a leak. In my case the problem proved to be the metal gaskets on both sides of the banjo bolt fitting at the fuel pump output. It would not leak unless the pump was running and producing pressure. I did not find the problem until I crawled under the car with the engine running.

The previous owner apparently reused the aluminum gaskets after changing the fuel filter. I replaced those gaskets and problem solved. The gaskets are available in aluminum or copper. I recommend copper and don't overtighten and don't reuse. They are cheap enough.

The bonus was improved mileage since I was not spraying the world with gasoline while underway.