I just repaired mine last night...I hope. Got mine for $10 at the last REI garage sale and it had no leaks/punctures/tears at first (checked in the tub and by laying on it an hour or so)... until I used it in the field... and it went partially flat on me (used schnozzle bag).
Came back to check again for leaks, with more thorough tub test and soapy water test... no punctures, etc... but just the slightest leak coming from the deflation valve, from within the plugged area. I ended up just smearing some seamgrip down in there, then plugging it up.
It held up overnight with ~ 60 pounds sitting on it without deflating, so I hope that's that. I'll just stick my finger down the inflate one-way valve to deflate from now on.
Hopefully your leak is a puncture or something, it'll be much easier to fix than a valve leak like mine.
Best of luck to you!