Hi, my W210 E320 CDi has this leak from the fuel filler cap area which I've read about and it seems the filler cap is the issue (it has a cheap after market one at the moment). I am going to source a dealer with this in stock and get one first thing in the morning and see if this solves the leak (I was quoted £24, but that dealer couldn't do anything till monday). Also, just to be sure, I'll check the flange that the cap's gasket seals onto, to see if it's been bent at all, as has also been suggested on other threads.

The twist in my case though, is I can't seem to fill the the tank more than about 3/4 full (it wasn't me who tried to fill the tank, but the person who did, has had many more years of tank filling experience than me, and filling a tank full isn't exactly rocket science....although having said that, I will still give it a go as well tomorrow and see what happens, after fitting the new fuel filler cap and checking the flange). I guess not filling the tank full while it is in need of a new fuel filler cap worked out to my advantage. But if it continues to do this, understandably, it's going to get annoying. So any ideas what may be causing this?

Also, I'm attaching a picture of the fuel filler area....I know this is pretty obvious, but just to be sure before I go checking it or sticking anything down it to make sure its clear, is the little hole that is underneath and to the right of the actual fuel filler tube (and circled in red in this picture) the drain? Because it has fuel/water standing in it. So if it is the drain, it's clearly blocked and needs clearing.

Thanks.

Baz.