This earlier thread regarding flex cracking on may be worth a read
http://www.walkingforum.co.uk/index.php?topic=37261.0Apart from drying the boots out slowly at the correct room temperature and storing them in correct conditioms applying an additional regular coat of a good leather conditioner such as Berghaus Leather Conditioner (if you can still find any) or Grangers Leather Conditioner across the flex points may also help.
Applying any leather treatment requires time and effort to really work the oils contained in the product down into the fibres of the leather and is best done by hand using the heat from your fingers.
In my experience a quick brush on and brush off is just not enough.When new Altberg boots arrive from the factory having had only minimal treatment and the leather is quite dry and it may require several coats to build up the initial level of waterproofing and conditioning to a satisfactory level.