parts needed for injector R&R

Do i need any new gaskets or o-rings to remove & replace injectors? 96 windstar 3.8 with 145000 miles, it has a slight ping on light acceleration, like the cruise control does to keep speed on overpass. at WOT it is fine. I don't know if the EGR passages have ever been cleaned, I didn't know to ask the mechanic when he replaced intake manifold gaskets a few years ago, no Check Engine light, runs fine otherwise.