[Desert Toad]

My water developed quite a leak the other day, draining all it could on my garage floor. According to the mechanic handbook, there should be a star packing nut to tighten things up. All I have is a collar with an Allen head set screw in it. I haven't been able to loosen it, afraid I might strip it out. Was this a normal thing, or did someone grabbed whatever would work once upon a time?

Thanks!