I’ve seen this mentioned in a few posts and wonder if another post I saw is related. That other post was about using Vinegar to clean parts with metal in them. Apparently Acetic acid will penetrate plastic, so can permeate the casing and get into the magnet itself. From there it causes rust. The recommendation is to use Hydrochloric (Muriatic) or Citrix acid to soak any parts that contain metal instead of Acetic. Acetic is fine to use on all plastic parts however.
I haven’t had experience with this myself, just passing this on.
I’m on my 3rd wet side, the first two both rusted at magnet. But keep on my mind my unit is one of the first generation with the blue driver, so it’s about 10yrs old.