Mag 12 question

[rattler]

I am replacing my front cover and impeller on my Mag 12 pump. The last one, the cover where the impeller fits in, had a moment and decided to wear away. This caused the impeller to not be centered in the magnets of the pump ( rattle,rattle.grind, grind). Do I add petroleum jelly to any parts of the impeller when I reassemble the pump? The new impeller seems very snug when fitted to the cap. I have already sanded the inside of the new cover to get rid of casting pieces. This was interfering with the rotation of the impeller when assembled. Thank you for your replies in advance.

Cheers!
Rattler