When you replaced the bad fuel injector make sure you did not pull the other injectors out. The o-ring can tear when you pull on it. Is a one use o-ring.
The fuel banjo fittings that goes to the fuel rail have copper gaskets on them. They usually need to be replaced because the get hardened, and won't seal again. Instead of replacement, you can also heat them up with a torch until is almost dull red and let it air cool again. Do the same with cold start injector.

Ben