scsims :
You should look into bentonite clay. It can be purchased in dry powder form from oil & gas drilling companies in 50lb. bags. You mix it with water and the goo like clay sinks to the bottom and toward the leak. When it gets there it fills the leak just like you had packed clay to start with. There are other posts on this site and an article in a recent PONDBOSS on bentonite. Good luck--ewest.