Ok you found some bubbles, or a blue streak don’t worry we can fix that.
1. Evaluate the leak. Where is the leak it, how do you think it happened etc. Very few leaks can be fixed from the outside. Smearing sealant on the outside of a rivet or seem will not be a long term fix. The easy way is to cut an inspection cover into the fuel tank back in the “bay” where the leak is. It can be the as big as the “bay” it is in.
It can be round or rectangular. Leave a minimum of 1 inch around the perimeter between skin and ribs to rivet and seal the new cover plate to. With the hole cut in the area that you think will allow best access, look for the leak. It will usually be a seam or rivet tail that isn’t fully covered with sealant. It sometimes is not directly at the leak. When you identify the leak clean the area with 100% Acetone and apply sealant neatly. When satisfied with the reseal, fabricate a cover with a ¾ inch over lap around perimeter and use a 1 inch rivet spacing. Seal the cover and rivet in place. Seal the seams and the rivet heads. Let sealant fully cure. Re-leak test. Then proceed per steps below.
