Since then I replaced with the fuel cap seal with a non-cork one and it's been perfect. Also a Mercedes part: 1404710079
That's the one to go for.
Use the original MB part (or equivalent). Never ever use cork again.
I put a bit vaseline (or MoS
2-containing black grease) on both sides of the gasket and it works perfectly. Very smooth locking of the cap on the filler neck and it's tight !
BTW, the A140 471 0079 is blue nowadays and resistant against modern fuel qualities what other (older) rubber gaskets might not be.
Best,
Achim
(fuelfillercapcollector)