I'd try some paint remover. The more aggressive the better. Try brushing it on, wait a few minutes for it to soften the sealer, agitate with a stiff bristled brush and wipe with rags. Several applications will probably be needed. You may not get 100% of the sealer up, but it shouldn't be nearly as obvious.

Methylene chloride paint stripper and a bristle brush.

Do not use a steel brush or you can end up with rust stains.