I have dry skin and cracks happen on my thumb all the time. They heal but then I bowl and it starts all over. What I found works for me:
After I get home, I put neosporen (sp) on the crack and leave a band aid on it over night. Take the band aid off after the second day and it seems to be better.
If it cracks open during bowling I have used everything you mentioned and the only thing that stops the cracking is super glue, very small drop on each side of the crack, NOT in it.
Nexcare makes a Skin Crack Care that you brush on but it won't hold up for more than one game. Nue Skin the same, won't hold up and clear nail polish works but burns like ...well, you understand.
Last option I have tried and it's a pure pain but the dry skin went away for a long time was to put skin lotion on at night and cheap plastic gloves on while I slept. That lasted a couple nights because I can't stand crap like that on my hand, the glove.
All I can say, Good Luck and DO NOT put the super glue into the crack, only on the ends so it won't crack more.
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az guy aka: R & L Bowlers Pro
rlbowlerspro@cox.net