If there is a leak at the back mount - it is a vibration/stress crack and it will not stop cracking unless you weld it. The bad thing about this kind of crack is that it can be located under the mount, and the only way to get to it is by carefully grinding away the welds and removing the mount.
Getting motorcycle tanks safe to weld is not a big deal, they are small and don't have any baffles to keep them from drying well. On the first day that you can work on it in the morning, and the sun will be out.....Drain the tank and shake out all the gas you can. Then use some full strength Purple Power or a similar degreaser mixed with an equal amount of really hot water....about a quart will do it.....and shake it around really well. Then dump that out and rinse with some really hot water. Then blow it out as best you can with an air compressor....it will likely flash rust (we can fix that during the coating process). The set the tank out in the sun to dry. At the end of the day pick up the tank, put your nose to the filler neck, and most likely you will not smell any fuel. If you have an aquarium pump they work great for supplying a small amount of air flow while the tank airs out.
Then you most likely will have to cut the mount off, fix the crack, and weld the mount back on.
I would then coat the tank as a precaution.....Here is the link for cleaning and you need to do some of this before the coating process.
http://suzukisavage.com/cgi-bin/YaBB.pl?num=1386849349My current favorite coating is the epoxy coating from Caswell Plating. Be sure to use it when the temperature and tank is warm - the stuff is really thick when cold and hard to get spread out all over the tank. The Caswell is an epoxy and most likely the most durable of any coatings. My next favorite is POR15, it has a nice silver color and sets up using moisture from the air....an aquarium pump really speeds up the curing process. The stuff like Cream and other white coatings have a acetone base....and Caswell and POR15 are far more durable.
You may want to buy or borrow a spare tank to use while you get this work done.....it will take a few days to clean, weld and coat.
Dave
I going to go find the link for the cleaning and coating the tank.