I'd stay away from methyl ethyl kill you. Almost anything MEK can do, acetone can do, with a fraction of the nasty factor. It carries away 'stuff' better and flashes quicker and cleaner, too.
Acetone and a rag, acetone and a white Schotchbrite, acetone and nylon cup brush if all else fails. (Hurt the adhesive with the acetone, then CAREFULLY knock it out with the cup brush, being careful not to get down as far as the fibers in the Hypalon.)
If it's Hypalon, the gold standard glue is Bostik 2402. Apparently very difficult to find in the US now. No idea what the next best is - last I bought it, I had a great source, so never needed an alternate.