The main problem with any boot, is that the outside material will always soak up the water eventually, and it is the waterproof liner that stops the water getting in.
With time though, the liner cracks, usually at the flex points like the ankle and toes, and this cannot be repaired.
If the boots are a total leather outer they can be kept waterproof as you would have done years ago, with dubbin, beeswax etc, but many synthetic/fabric boots that wont work as well with fabric waterproofers.