Probably a dirty/corroded electrical connector to injector not injector itself.
If possible try to wiggle connectors when engine miss firing to see if you can tell which one it is.
I usually can figure out which this way if one cylinder injector connector is causing missing.
If connectors are type with thin wire locks remove them with "dental pic" or small electricians screwdriver and remove connector and inspect for green corrosion on injector pins and connector terminals. If corroded clean with electronic spray cleaner and small brush, etc.
I see your fuel injector connectors are of a better design with quick disconnect spring locks that are easier to unlock than older models. I added them to my 164 when I replaced corroded injector connector wiring.
It is always possible that you have a bad injector if wiring connectors OK but maybe not.
As for your spark plug wire I would have to see other end on sparkplug but I would think you could use a standard wire but if yours has a resistor in end then the replacment wire should match that kind.
As for fuel leak you need to verify where leak coming from - hose, fuel rail or injector. Yes a fuel leak is something that needs to be fixed as it could leak down onto hot exhaust pipe under engine.