After 4 years in salt service, my oldest Super Duty G showed its first rust sign - only in the magnets (everything else all through the reel looks pristine).
This is filliform corrosion - sideways under a coating - a mechanism for a little bit of salt from the air, combined with condensation, to concentrate in place - and you can't remove it, without removing the coating (which is there to protect the magnets, etc.)

I did clean and rebuild the whole brake plate, and everything inside was pristine

I ordered Momo N52 magnets through Ali Express (AMO store). While their piece-price on these looks dirt cheap, they hit you with a big shipping charge.
I ordered 8, and they came prepackaged as 10 - the $17 total price was still fair.
Those are not the original spool bearings, but unshielded Air HD (rust resistant) I swapped in 2 years ago for longer casts - they're faring quite well, and of course they get flushed every time they get oiled.

The Momo N52 magnets are gold-plated - will be interesting to see how this fares compared to the coating on the stock magnets.
These magnets are powerful. In my 1/4-oz niche on the 8 old magnets, I had the mag set a notch above 50% for total-reliable casting, and great cast distance.
Test casting with the 8 new magnets, incipient backlash was only about 20% mag adjustment, and the next two notches were excessive step changes on the cam - too much mag.
So I took two magnets out.
Trying again, didn't cast or adjust enough to find incipient backlash, but was getting 120' reliable cast at a little over 40%, and several notches in that range felt better graduated - that is, narrow changes in mag over several notches. And plenty of adjustment left to add mag for casting 1/8 oz.

The importance of getting salt rust out of a reel can't be overstated.
Salt rust is more corrosive than salt itself, and you don't want it moving around inside your reel. (I'm a metallurgist and corrosion engineer)
Many metals are resistant to salt, but salt rust carries hydrochloric acid, and those same salt-resistant metals will be attacked.
While I was buying, I bought the HCRB (Daiwa mag seal) ball bearing replacements for the last 3 shielded drive bearings in the reel (worm shaft and main drive shaft).
But the original bearings still look so good, I stashed the new bearings in the reel box for later.