Im no expert but if it has never been full its not a leak problem. My pond will over flow over the top of my damn when we get a good rain. A pond that size should be able to fill up pretty ease with a good rain even with a leak. My best guess is you dont have a big enough water shed to fill it up.

The people who say I can't do it can just sit the @^#% down and watch me. Friends call me Rusto I also subscribe to pond boss mag. http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=504716#Post504716