As above really, what does everyone use? Mine are leaking through a crease just behind the toe cap
I have always used sump oil , never found anything better on boots regularly getting wet.Many years ago I got a boot covered in hydraulic oil.
When the other one was tatty and split a year or so later the oily one was still as good as new.
Since then I've tried to give my boots a bit of treatment every now and then.
Leather soap for saddles is what I use at the moment, but nothing seems to have ever worked as well as that proper soaking in oil.