Friend has a 1996 454 Mag MPI with a leaking injector at the rail. I assume there is a o-ring that seals the injector at the rail? I also assume that the intake plenum and fuel rail has to be removed to remove the injector and replace the o-ring???

you are correct. You can probably go to your local Fuel Inj shop and find replacements for all. Screens, too. Might not be a bad idea to have them cleaned if they're out.

NAPA has the top and bottom o-rings for about 4 bucks an injector.

Thanks guys. Motor was just rebuilt and he thought it had a gas smell from day one. It kept getting worse and he finally tracked it down to the injector this weekend. I am sure the builder will cover it but he has plans this weekend.