Having just finished a tank I have mor experience than I'd like....
MEK is the big gun, but it is NASTY. Have breathing protection and lots of ventilation. A little wiping will remove even dried sealant if its just smeared on the skin.
Lacquer thinner is what I use for sealant that is still wet or not as stubborn. Still not nice studf but not nearly as nasty as MEK.
On a side note, I left the proseal on a lot of clecos and they still work great AND don't scratch aluminum going in. They oughta make em that way.
Lastly, fast orange hand cleaner works fairly well with some scrubbing. I gave up on gloves after the 50th pair in 5 minutes and just clean my hands up at the end of each session.
Chris