I've got what you need (can mail it to you also if you prefer).
Mag 3 & 5 use the same impeller, and Mag 5 & 7 use the same impeller cover/o-ring.
If your pump is rattling, open it up and take a look at the impeller cover. 9 times out of 10, the impeller cover breaks where the little rubber bushing on the end of the impeller shaft sits, which causes the impeller to "play" and rattle. Left like that, it will kill the impeller eventually, and in worst cases, the pump itself, if the impeller housing on the pump, wears to the point where it's not cylindrical anymore (have seen that...).
I have impeller and impeller cover for Mag 5 here, just let me know.
Jenn