Guys, please answer my question I posted above.
Christmas is a bad day this year for me, I think. :(
I think that what you're calling "cracking" is just the buildup of the cordovan oils in the folds. Brushing, cleaner, etc. should remove it.
For the record, I have the same issue of one shoe shining up nicely and the other staying dull with a pair I got off of ebay. I figure I'll just keep brushing them and hope for the best, but they're awesome even partially shined.