I would not have thought that the bellows on either of these cameras is actually 'leather'. On my Zeiss Super Ikonta it most definitely isn't. You can test this easily by gently flicking a finger over the inside of the bellows and if there is a dry papery sound then it isn't leather. Leather will be almost soundless.
On a large format camera 4x5 and upwards they bellows may very well be of leather because they can take the extra bulk and they are not folded shut so often..
To be light tight, the leather would have to be too thick to be of any practical use and make folding the camera front a difficult operation. It is more likely to be a fine woven fabric base covered over with a hard wearing material that looks very much like leather just as on my Ikonta.
I would not like to put any preparation on the bellows as it will have some grease content, and as we know grease can migrate to places it isn't needed.