dumb question, but should the rubber pad be removed when you install the tank?
also:
http://www.klr650.net/forums/showthread.php?t=89692
http://www.klr650.net/forums/showthread.php?t=10875
http://www.google.com/webhp?sourceid...&bih=809&ion=1
IMS has been pretty good about replacing the tanks at a very reasonable cost, mostly shipping plus a few $$$. How thick is the plastic where it broke? IMS has also been known to have tanks of varying thickness, to the point that it actually impacts fuel quantity, is it possible that you happen to get the one tank that was thin at that very spot?