I wasn't going to post this because fuel tanks should really never be fixed unless they are for a special car or truck. Most of the time it pays to replace the fuel tank when it has leaks. That said, I decided to fix this one because a new one would have been around $500, and that was just a little too much.
NOTE: For safety purposes, I didn't post the entire detailed procedure because I don't want anyone trying this themselves unless they are trained to do it. If you're not trained in the cleaning, inert gassing and soldering procedures then you should take it to a specialized shop that is qualified to do this work.
Jaguar E-Type gas tanks are notorious for leaking at the lower inner corner. The reason is that condensation accumulates in this area and the OEM fuel tank cushion pads that are installed in this area absorb the condensate and wick the moisture to cause rust.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3175%20Medium.jpg)
Look at the pitting -- I don't even have to strip the paint to tell that there are pinholes underneath that pitting.
I first removed the sending unit and dropped a chain into that part of the baffle. Shaking and turning the tank over and over will knock a lot of the interior rust and corrosion loose to expose more of the damaged areas. Then I strip the exterior paint with a wire wheel -- and PRESTO!! -- lots of pinholes and enough pitting to cause many more pinholes in the future.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3176%20Medium.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3177%20Medium.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3178%20Medium.jpg)
The entire area will have to be stripped to bare metal and a patch installed.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3179%20Medium.jpg)
This is 1/16" lead sheet that I keep around for gas tank soldering. I cut an appropriate patch to size with tin snips and start to prep the sheet.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3180%20Medium.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3181%20Medium.jpg)
The bulk sheet must be made stretchable by hammering and flattening sheet until it becomes wider, thinner and more flexible. It takes a flat faced hammer to expand and stretch the lead into a proper patch. Then the patch is formed to match contours of the lower tank corners. At this point you can form it pretty much by hand.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3182%20Medium.jpg)
Then the metal is first cleaned with a strong solvent and then the area is tinned with some body soldering "tinning butter"
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3183%20Medium.jpg)
Next I use my propane torch and a lead body solder bar to solder the patch along its seams. Once the soldering is done, I give it a quick scuff with a 60 grit sanding disc and make sure all the seams are nicely filled in.
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3186%20Medium.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3184%20Medium.jpg)
(http://i357.photobucket.com/albums/oo18/goodfellow_2004/Jaguar/Fuel_Tank/PICT3185%20Medium.jpg)
Done -- took about an hour to lead this patch in. Finally I filled the tank with water and will let it sit overnight over a paper towel to see if there are pinholes in the leaded patch seam.
Although it only took and hour to solder, to prep the tank for this procedure took a lot of time over this last week, and I wouldn't recommend anyone trying this without knowing the proper safety procedure and techniques. Things can go seriously "BOOM" if this isn't done properly and by the book.