Just a quick one - is there a general consensus as what the foam pads on the top and bottom of the tanks actually do? If its sound insulation surely the sides would make more noise if petrol was sloshing, and I've never had a problem with noisy tanks before. Dynamat would be a better option if this is the case.

If it's just to provide a little more vertical clamping force then you don't have to cover the entire surfaces surely?

On my tanks the notion that the foam was trapping water and causing rust was completely erroneous - they were clean and smelled new! The small amount of corrosion was water being trapped in the "U" channel of the door rubber section pushed onto the welded flanges (what the tank really sits on)

The bits of foam from mine were bloody great at starting the bonfire 

So you finally came to your senses and torched it?

Nope - still sacrificing £20 notes at regular intervals to try and get some life back into her!!!

we do have progress - fingers crossed

On 13/03/2016 at 10:37, lotus4s said:

While certainly leaking window seals can be a problem, on the several S4 and S4s's that I have pulled rusty tanks from, the window seals were perfectly intact. It appeared that the water ingress was through holes in the body at the fuel filler. In the pics below there is evidence of water dripping on the mounting bracket for the tank cover which is directly below the fuel filler opening. 

 

 

Jim,

 

You are absolutely CORRECT !  "Windows leaking " is a Fairy Tale.

I have sealed off this gap with RTV

When fitting the fuel pump assembly always remove the pulsator damper and replace the connecting hose, no matter how "good" it looks.
Use ONLY "submersible" or Fluoroelastomer (Viton) hoses. Gates 27093 is the right dia,  5/16" ID. Do not use non submersion rated fuel lines inside the fuel tank as the outside will get eaten over time and you will have a very bad day.
Regular fuel hoses have gasoline resistant ID layer, BUT the outside skin is NOT SUITABLE for continuous petrol immersion.