I have a 1981 240D and live in Portland, OR. After putting in 3/4 tank of bio the other day the attendant did not replace the fuel cap correctly. The car leaked out the rubber hose below the tank near the right rear wheel and slowly stopped once I put the cap on correctly, later that day. This morning I have a new leak going- now it is coming out of the hole behind the right rear wheel under the fender which seems to be part of the body or undercarriage. Is this a run-off hole or vent hole or? Does it have to do with the cap not being on and driving around 10 miles? Thanks....

 

Just figured it out today. In Oregon you don't have to pump your own fuel at gas stations.
The attendent didn't put my cap on all the way so diesel leaked out the side of the car and also leaked out of the overflow hose near the right rear wheel. Meanwhile, inside the door near the fuel cap is a vent hole which is jammed with junk. As the fuel leaked out the cap, it some how diverted itself from the vent and ran through the gasket around the fuel intake and ended up in the trunk! Now I have diesel in the right side of my trunk and once I clean it out, along with blow compressed air from the overflow hose upwards towards the fuel intake, I should be clear. Lesson learned- fasten the fuel cap correctly.