If it is leaking from the top, then a set of o-rings should sort out your issues.
What you will probably find if it is leaking from the bottom is that it is coming from the centre section of the injector body, where the plastic casing and metal assembly meet. From dim and distant memory mine looked like it was coming out some sort of casting flash on the side. Had 2 leaking I think.
If that is the case, then either isolate the leaking ones and replace with tested good ones, or use it as an opportunity to upgrade.. I bought a set of 700 sards, and to go with it a PFC, and to go with that, a set of -5's, and to go with that........