Hello
It is a common problem indeed.
Had same problem. The pressure pipe from the top of the pump assembly was cracked a little. From here comes the leak. The black ring that holds the pump assembly on tank was cracked too.
You can see here how the pressure pipe can be repaired, there is another solution, on the forum, with brass and some special epoxy glue, but for some reason I can't find it today.
http://www.espacefreunde.de/forum/index.php/m/116918/?srch=reparatur+benzin+pumpe#msg_116918--------------------------------------------------------------
Last minute edit: I have browsing the link above, and I don't recommend this. The inner diameter of pipe is reduced, so the flow of fuel is reduced also. This repair might not be as good as it seems.
Anyway, in this link, you have pictures with faulty pressure pipe.
... and I have found it
http://www.espacefreunde.de/forum/index.php/m/115774/another here
http://www.espacefreunde.de/forum/index.php/m/161396/--------------------------------------------------------------
Mine have same "click" connectors. I don't think they are faulty.
Personally I bought a new pump assembly and replaced the cracked one. It was a bargain, aprox 100 euro. That was happened exactly in mid of june last year. I kept the old pump assembly.
The black plastic ring is the same on certain models of Twingo. The pump assembly was fitted by Matra/Renault only on JE and Avantime.
The phenomenon is quite complex... or simple?!?!?! . Roy can correct me, or anybody if I'm wrong.
When Loosen the cap from the tank to refill with gasoline at gas station, a lot of air came out of the tank.
A question here: Those with petrol engines. Do you have the same experience?
From here starts my hypothesis.
So, the tank is expanded almost all time. There is little room between top of the pump assembly and metal chassis of the car (1-3 cm). When pump starts, the tank is inflated, and this space is reduced to zero. I think ?!?!
The "click" connector of pressure pipe is bulky, and is the first, who reach the metal floor of the car when tank is inflated, with the "help" of nervure. The tension is passed to the pressure pipe, which has no reinforcement.
The protective cover of the pump assembly is made from flexible plastic, and playing no role in protection of the pump assembly pipes. On the contrary the plastic nervure put a lot of pressure on the "click" connector.
Bad design ?
Again I'm not working for FBI
and I'm not a mechanical engineer. This are my pure suppositions. Anyone can correct me.