Ghost overflow cleaning issue

[kris2001]

Hello Guys. I'm scrubbing away at my ghost overflow lid, which has a pesky snail infestation and enough mineral buildup to qualify as concrete. How can I blast it clean with vinegar or acid without nuking the magnets?
Even scraping it was not very effective

 

[fushi]

Hello Guys. I'm scrubbing away at my ghost overflow lid, which has a pesky snail infestation and enough mineral buildup to qualify as concrete. How can I blast it clean with vinegar or acid without nuking the magnets?
Even scraping it was not very effective

Pictures are always helpful.

Citric Acid is less determental than vinegar to plastics.