Fuel leak in the rear wheel well

[Jugostran]

Hey all, hope you're all doing great.
Recently I've been talking to someone who works on BXs, and I asked about rust in the rear wheel well (behind the fuel door) as it is a common spot for BXs to rust.
They told me that the issue lies with the fuel tank. Ergo, when the fuel tank is filled up all the way, some of the fuel splashes back (when cornering for example) and leaks over the inside of the wheel well. According to them, if this goes on for long enough, the fuel will strip all the factory rust protection leaving bare metal exposed. This of course leads to rust.
Is any of this true? I asked if it was fixable and was told it wasn't.
Interestingly enough, the person who sold me the car initially also warned me not to fill the tank up past 3/4.

[Jaba]

There is nothing open to the atmosphere in the wheel arch on the filler side. There is an anti spillage valve mounted there above the level of the auxiliary fuel tank and this can theoretically leak a bit of fuel, not in the arch though as it has a spillage tube connected to its output that vents into an open T piece, near the rear sphere, which is strapped to the petrol hose leading to the main petrol tank where there is no body seal to be found at all. I think its main function is to allow air in as the fuel level goes down.
They can drop off when the mounting point rusts through and falls off so perhaps this is where the urban myth comes from.
They do rust through on that side as the auxiliary fuel tank acts as a mud trap. It pays to clean it off regularly. Diesels rust there as well as petrol. I always fill mine right up cos I know it is petrol tight.

[Jugostran]

There is nothing open to the atmosphere in the wheel arch on the filler side. There is an anti spillage valve mounted there above the level of the auxiliary fuel tank and this can theoretically leak a bit of fuel, not in the arch though as it has a spillage tube connected to its output that vents into an open T piece, near the rear sphere, which is strapped to the petrol hose leading to the main petrol tank where there is no body seal to be found at all. I think its main function is to allow air in as the fuel level goes down.
They can drop off when the mounting point rusts through and falls off so perhaps this is where the urban myth comes from.
They do rust through on that side as the auxiliary fuel tank acts as a mud trap. It pays to clean it off regularly. Diesels rust there as well as petrol. I always fill mine right up cos I know it is petrol tight.

That's good to hear!
I think it is just that, an urban myth.
I have been filling it up to the top for the better part of a year now and never have I seen or smelled any fuel in that area.
So I think it is just the auxiliary tank (which I didn't know existed ) trapping dirt (which was my initial theory before I was told about the myth).