Originally Posted by Diesel911

If a shop did the work you should take it back to them and let them fix it. If you mess with it you will void any warranty.
Some possible causes of leaks between the injector nut and upper body are a hairline crack in the nut, improper torque, poorly lapped surfaces in the interior parts of the injector and something got caught between the lapped surfaces when the assembled the injector.
If there is something caught between the surfaces tightening it more will only make it worse. If the surfaces were not lapped well tightening it may not help either.