Mag drive pump impeller

Is it spring yet.
been -10f for the last week.

When I shut down my pond last fall, I took the housing off of my MAG 1800
pump.
I noticed that the shaft was a little rough to slightly gouged in the center
of the shaft but no more than an 1/8 inch deep. Must have ground up some
snails that got in there.

As I was shopping for replacement pads for my skimmer I noticed that they
also have replacement impellers.

My pump is two years old.
When if ever and why would you need to replace an impeller in a Mag Drive
pump???
Do they need to be replaced because the magnets wear out???

Too cold to pond but I can drean and plan for next year.

Zone 4
NW Iowa

JROCK
..