Paint thinner/ mineral spirits, NOT lacquer thinner, and a couple of cheap soft bristled brushes. The paint thinner will not harm the seal.

If you're, ahem, "frugal" like me (cheap) then you can save the dirty solvent in a glass container, cap it and let the sediment settle to the bottom (takes a couple of days). You can then pour off the relatively clean top layer and store it for re-use as a cleaner.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now