I’m not so sure about the long term stability of that coating. There are other causes for loss of sensitivity, assuming that you’re only using it as a sensing magnet but if you’ve lost lifting power, get it replaced.
I suggest reading this thread about another magnet that had issues:
Hell no. Magnets dont lose that significant * power over time. That this is cracked and rusting inside I’m betting.
Get it taken out by a pro ASAP… if you ask me
* I guess if you come here to ask, it’s already significant enough to worry you, idk, not 1% loss but rather a lot more, which in (almost) all of the cases I have read about meant → it had to be taken out sooner or later