[SEO9C1]

I pulled my fuel rail today and realized that these were removed at one time by me. I don't remember doing it but I have read multiple threads where people say to use them and or not to use them.

I'm running into a weird vacuum leak on the car and I want to rule this out as one of the issues. Should I track down a set or not worry about it?

+1 here for using them. They stabilize the injectors to the rail. Install the injectors onto the clips and then drop the whole assembly into the ports guiding them in as you go along. Don't attempt putting the injectors into the ports and then seating the clips on after the fact. The former assures the injectors are stabilized between the rail and the ports. The latter just tears the clips up and they don't seat properly. Assuring there are no leaks is paramount. You don't want an engine fire, yes? Use new O-rings w a light coating of dialectric grease or similar to seat the injectors to the ports.

The fuel rail/injectors have nothing to do with vacuum. The only vacuum related item is the hose connecting the regulator to the intake manifold.