I doubt that pulling the magnet would de-magnetize it; the base was probably built by inserting a magnet into the housing. Still, to be safe, you could try softening & flushing out the old grease with a wash bottle filled with a petroleum based solvent, NOT acetone. My preference for things like this is whatever version of mineral spirits is cheapest!?
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(That's a short version of a horribly long link; you can avoid it by searching for, "wash bottle" & picking the cheapest - it should cost under $2, no need for an over priced one.)
You'll probably also want some non-magnetic tools to help dig the old grease out.
Roy
