Replacing the O-rings is a good idea. Usually they come in a kit including the plastic cap of the injector. Just clean it out the best you can with carb cleaner or injector cleaner.
agreed. a shop can clean and flow them, but it is usually cost prohibitive unless you have a hook-up.
some folks like to use hot water when installing the pintle caps. you can get the Borg Warner kit with o-rings and pintle caps for a few bucks each at parts stores.