This is a very common Ford problem, and not just the F-series. It's almost always the passenger rear too.
Before installing the new injector, use sensor safe grease or cooking oil to lubricate the o-ring, or you will almost always destroy it when completing the install.
This is also the most common cause of Ford engine compartment fires, and as we all know, after 10 years, Ford will recall any parts and melt them down to make parts for lease vehicles. The rule of thumb is that if you plan on owning your vehicle for over 10 years, then NEVER buy a Ford. Their policy is to abandon customers who purchase in lieu of lease vehicles. Literally melting down old stock parts to make parts for newer vehicles. Don't believe me? Try to find a part for a 10 year old vehicle. Here, try this part, the stud bolts for the upper intake manifold to lower intake manifold which are required to be replaced anytime you replace an injector or upper or lower intake gasket, plenum gasket. p.s. the plenum and intake gaskets are only good for 2-4 years. W702312-S309M << Ford part number for the bolts that Ford require replacing when doing a gasket or injector, otherwise an engine fire can occur.