If someone has reported a leak on a seam are they/you sure that is indeed the case.
Before you go the expense of replacing the tank , take a very good look at the hoses. You might have to remove some shielding behind the spare wheel carrier to look at it. There is often some chaffing , possibly due to between the tank mounted on the chassis and the filler cap mounted on the body, similar cause to DaveW mentioned above.
If all the hoses are fine , and the seam leak is confirmed I would definitely go to Simon for a replacement tank. Consider getting a stainless one for extra long life.
