Yeah, good idea. I've never seen this. Didn't even know that coral could produce slime or whatever.
Actually, i just did some reading up and your monti may have STN. STN is slow tissue necrosis. Its when stony coral lose tissue slowly and it says that when STN occurs and tissue is slowly being destroyed, slime will be produced by the monticap.. There's no solution or cure, but people have had some success by fragging off the parts that have slime on them, and are being eaten away. But they say that even then, it may not stop STN from happening to the rest of the monti.