1969 Dart Street/Strip (Re)Build

What ball joint are you using Clint? They pretty much all do that with aftermarket arms. The threaded cup is taller than the stock mounting point and doesn't let the boot push up and seat the way is supposed to. The QA1 ball joints do have a nice dust boot that actually stays on and seals up, you could try those if it bothers you too much. The QA1's the body is actually longer i believe so it comes past the threaded cups you get with aftermarket arms and allows you to seal the boot.