Moisture wicked through the inner Gortex layer inside a boot does not pass through the leather at all, but rises between the inner liner and the outer ( leather) shell of the boot. This is why they are separate. Any substance, polish, dubbin or leather grease (Leder Gris) creates a barrier against water, either way.
If you place a piece of Gortex and a piece of Cordura over your mouth and blow, air will pass. Try breathing though leather, best of luck!
All my work and bike boots get cleaned under a tap with a scrubbing brush and then treated with Scarpa leather cream. I took a picture how sad is that. I've used it for years.
Not much point having the moisture from you foot pass through a goretex membrane only to find it can’t get out through the pores in the leather!
I haven't used dubbin for at least 40 years when the wisdom was that it rots cotton stitching in the boot. Nikwax replaced it for me but nowadays I stick to Leder Gris or the Daytona stuff from a tube which smells like honey.
Exactly. In the same way a goretex jacket will work better if it is clean and the moisture can pass through the gore tex and then out through the outer layer. It is not the leather treatment on a goretex lined boot that makes it waterproof, it is the goretex. No point in slapping stuff all over the boot at all....all you need to do is stop the leather drying out and cracking.
But, since apparently I am wrong, we'll maybe leave it the experts...
I am afraid you are wrong. Gortex is the material liner on the inside of the boot, as with a Gortex liner in a jacket. Whatever you put on the outside will not affect the Gortex. However, the Gortex on the inside of a boot will have a finite life and once reached will then be ineffective.
The GoreTex liner is indeed on the inside of the boot (and may or may not be bonded to the actual leather depending on the boot). So whatever you put on the leather will not affect the GoreTex at all. However - it may impact the ability of the GoreTex to allow moisture out of the boot.
So if you clog all the pores of the leather, your feet may get damper through sweat not being able to evaporate through the membrane.
In practice however, you would probably never notice this - unless your boots were perforated leather (which is unusual, but not unheard of in a waterproof boot) and you had clogged the holes with dubbin/polish/wax/whatever.