leaking fuel sending unit

Guys I need some quick help! I just had my fuel sending unit replaced by a shop, I filled 10 gallons of gas in it and it's dripping like niagra falls. How could they screw up so bad. The shop is to far to drive or tow to, so I'd like to do it myself. Could the seal be put in wrong and if I replace it, could I use some kind of compound to help seal the unit when I connect it back up?

Thank you...always something :)