DD1 sucked hers til she was 26 months, we had only one infection in that time and it was in the cuticle, we had to use betadine on it then rinse well. as for stopping her, we used sports tape on her thumb as we knew it wouldnt come off and it was uncomfortable so she couldnt suck it, it worked!!
as for the split, thats a tough one im afraid, is it a bad split??